iommu/vt-d: debugfs: Fix legacy mode page table dump logic

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

iommu/vt-d: debugfs: Fix legacy mode page table dump logic

In legacy mode, SSPTPTR is ignored if TT is not 00b or 01b. SSPTPTR
maybe uninitialized or zero in that case and may cause oops like:

Oops: general protection fault, probably for non-canonical address
0xf00087d3f000f000: 0000 [#1] SMP NOPTI
CPU: 2 UID: 0 PID: 786 Comm: cat Not tainted 6.16.0 #191 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-5.fc42 04/01/2014
RIP: 0010:pgtable_walk_level+0x98/0x150
RSP: 0018:ffffc90000f279c0 EFLAGS: 00010206
RAX: 0000000040000000 RBX: ffffc90000f27ab0 RCX: 000000000000001e
RDX: 0000000000000003 RSI: f00087d3f000f000 RDI: f00087d3f0010000
RBP: ffffc90000f27a00 R08: ffffc90000f27a98 R09: 0000000000000002
R10: 0000000000000000 R11: 0000000000000000 R12: f00087d3f000f000
R13: 0000000000000000 R14: 0000000040000000 R15: ffffc90000f27a98
FS: 0000764566dcb740(0000) GS:ffff8881f812c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000764566d44000 CR3: 0000000109d81003 CR4: 0000000000772ef0
PKRU: 55555554
Call Trace:
<TASK>
pgtable_walk_level+0x88/0x150
domain_translation_struct_show.isra.0+0x2d9/0x300
dev_domain_translation_struct_show+0x20/0x40
seq_read_iter+0x12d/0x490
...

Avoid walking the page table if TT is not 00b or 01b.