drm/amd/display: Fix NULL deref in debugfs odm_combine_segments

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix NULL deref in debugfs odm_combine_segments

When a connector is connected but inactive (e.g., disabled by desktop
environments), pipe_ctx->stream_res.tg will be destroyed. Then, reading
odm_combine_segments causes kernel NULL pointer dereference.

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 16 UID: 0 PID: 26474 Comm: cat Not tainted 6.17.0+ #2 PREEMPT(lazy) e6a17af9ee6db7c63e9d90dbe5b28ccab67520c6
Hardware name: LENOVO 21Q4/LNVNB161216, BIOS PXCN25WW 03/27/2025
RIP: 0010:odm_combine_segments_show+0x93/0xf0 [amdgpu]
Code: 41 83 b8 b0 00 00 00 01 75 6e 48 98 ba a1 ff ff ff 48 c1 e0 0c 48 8d 8c 07 d8 02 00 00 48 85 c9 74 2d 48 8b bc 07 f0 08 00 00 <48> 8b 07 48 8b 80 08 02 00>
RSP: 0018:ffffd1bf4b953c58 EFLAGS: 00010286
RAX: 0000000000005000 RBX: ffff8e35976b02d0 RCX: ffff8e3aeed052d8
RDX: 00000000ffffffa1 RSI: ffff8e35a3120800 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff8e3580eb0000 R09: ffff8e35976b02d0
R10: ffffd1bf4b953c78 R11: 0000000000000000 R12: ffffd1bf4b953d08
R13: 0000000000040000 R14: 0000000000000001 R15: 0000000000000001
FS: 00007f44d3f9f740(0000) GS:ffff8e3caa47f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000006485c2000 CR4: 0000000000f50ef0
PKRU: 55555554
Call Trace:
<TASK>
seq_read_iter+0x125/0x490
? __alloc_frozen_pages_noprof+0x18f/0x350
seq_read+0x12c/0x170
full_proxy_read+0x51/0x80
vfs_read+0xbc/0x390
? __handle_mm_fault+0xa46/0xef0
? do_syscall_64+0x71/0x900
ksys_read+0x73/0xf0
do_syscall_64+0x71/0x900
? count_memcg_events+0xc2/0x190
? handle_mm_fault+0x1d7/0x2d0
? do_user_addr_fault+0x21a/0x690
? exc_page_fault+0x7e/0x1a0
entry_SYSCALL_64_after_hwframe+0x6c/0x74
RIP: 0033:0x7f44d4031687
Code: 48 89 fa 4c 89 df e8 58 b3 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00>
RSP: 002b:00007ffdb4b5f0b0 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f44d3f9f740 RCX: 00007f44d4031687
RDX: 0000000000040000 RSI: 00007f44d3f5e000 RDI: 0000000000000003
RBP: 0000000000040000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007f44d3f5e000
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000040000
</TASK>
Modules linked in: tls tcp_diag inet_diag xt_mark ccm snd_hrtimer snd_seq_dummy snd_seq_midi snd_seq_oss snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device x>
snd_hda_codec_atihdmi snd_hda_codec_realtek_lib lenovo_wmi_helpers think_lmi snd_hda_codec_generic snd_hda_codec_hdmi snd_soc_core kvm snd_compress uvcvideo sn>
platform_profile joydev amd_pmc mousedev mac_hid sch_fq_codel uinput i2c_dev parport_pc ppdev lp parport nvme_fabrics loop nfnetlink ip_tables x_tables dm_cryp>
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:odm_combine_segments_show+0x93/0xf0 [amdgpu]
Code: 41 83 b8 b0 00 00 00 01 75 6e 48 98 ba a1 ff ff ff 48 c1 e0 0c 48 8d 8c 07 d8 02 00 00 48 85 c9 74 2d 48 8b bc 07 f0 08 00 00 <48> 8b 07 48 8b 80 08 02 00>
RSP: 0018:ffffd1bf4b953c58 EFLAGS: 00010286
RAX: 0000000000005000 RBX: ffff8e35976b02d0 RCX: ffff8e3aeed052d8
RDX: 00000000ffffffa1 RSI: ffff8e35a3120800 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff8e3580eb0000 R09: ffff8e35976b02d0
R10: ffffd1bf4b953c78 R11: 0000000000000000 R12: ffffd1bf4b953d08
R13: 0000000000040000 R14: 0000000000000001 R15: 0000000000000001
FS: 00007f44d3f9f740(0000) GS:ffff8e3caa47f000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000006485c2000 CR4: 0000000000f50ef0
PKRU: 55555554

Fix this by checking pipe_ctx->
---truncated---