vdpa/mlx5: Fix invalid mr resource destroy

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

vdpa/mlx5: Fix invalid mr resource destroy

Certain error paths from mlx5_vdpa_dev_add() can end up releasing mr
resources which never got initialized in the first place.

This patch adds the missing check in mlx5_vdpa_destroy_mr_resources()
to block releasing non-initialized mr resources.

Reference trace:

mlx5_core 0000:08:00.2: mlx5_vdpa_dev_add:3274:(pid 2700) warning: No mac address provisioned?
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 140216067 P4D 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 8 PID: 2700 Comm: vdpa Kdump: loaded Not tainted 5.14.0-496.el9.x86_64 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
RIP: 0010:vhost_iotlb_del_range+0xf/0xe0 [vhost_iotlb]
Code: [...]
RSP: 0018:ff1c823ac23077f0 EFLAGS: 00010246
RAX: ffffffffc1a21a60 RBX: ffffffff899567a0 RCX: 0000000000000000
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000000000000000
RBP: ff1bda1f7c21e800 R08: 0000000000000000 R09: ff1c823ac2307670
R10: ff1c823ac2307668 R11: ffffffff8a9e7b68 R12: 0000000000000000
R13: 0000000000000000 R14: ff1bda1f43e341a0 R15: 00000000ffffffea
FS: 00007f56eba7c740(0000) GS:ff1bda269f800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000104d90001 CR4: 0000000000771ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:

? show_trace_log_lvl+0x1c4/0x2df
? show_trace_log_lvl+0x1c4/0x2df
? mlx5_vdpa_free+0x3d/0x150 [mlx5_vdpa]
? __die_body.cold+0x8/0xd
? page_fault_oops+0x134/0x170
? __irq_work_queue_local+0x2b/0xc0
? irq_work_queue+0x2c/0x50
? exc_page_fault+0x62/0x150
? asm_exc_page_fault+0x22/0x30
? __pfx_mlx5_vdpa_free+0x10/0x10 [mlx5_vdpa]
? vhost_iotlb_del_range+0xf/0xe0 [vhost_iotlb]
mlx5_vdpa_free+0x3d/0x150 [mlx5_vdpa]
vdpa_release_dev+0x1e/0x50 [vdpa]
device_release+0x31/0x90
kobject_cleanup+0x37/0x130
mlx5_vdpa_dev_add+0x2d2/0x7a0 [mlx5_vdpa]
vdpa_nl_cmd_dev_add_set_doit+0x277/0x4c0 [vdpa]
genl_family_rcv_msg_doit+0xd9/0x130
genl_family_rcv_msg+0x14d/0x220
? __pfx_vdpa_nl_cmd_dev_add_set_doit+0x10/0x10 [vdpa]
? _copy_to_user+0x1a/0x30
? move_addr_to_user+0x4b/0xe0
genl_rcv_msg+0x47/0xa0
? __import_iovec+0x46/0x150
? __pfx_genl_rcv_msg+0x10/0x10
netlink_rcv_skb+0x54/0x100
genl_rcv+0x24/0x40
netlink_unicast+0x245/0x370
netlink_sendmsg+0x206/0x440
__sys_sendto+0x1dc/0x1f0
? do_read_fault+0x10c/0x1d0
? do_pte_missing+0x10d/0x190
__x64_sys_sendto+0x20/0x30
do_syscall_64+0x5c/0xf0
? __count_memcg_events+0x4f/0xb0
? mm_account_fault+0x6c/0x100
? handle_mm_fault+0x116/0x270
? do_user_addr_fault+0x1d6/0x6a0
? do_syscall_64+0x6b/0xf0
? clear_bhb_loop+0x25/0x80
? clear_bhb_loop+0x25/0x80
? clear_bhb_loop+0x25/0x80
? clear_bhb_loop+0x25/0x80
? clear_bhb_loop+0x25/0x80
entry_SYSCALL_64_after_hwframe+0x78/0x80