wifi: mt76: mt7921: fix kernel panic due to null pointer dereference

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

wifi: mt76: mt7921: fix kernel panic due to null pointer dereference

Address a kernel panic caused by a null pointer dereference in the

`mt792x_rx_get_wcid` function. The issue arises because the `deflink` structure

is not properly initialized with the `sta` context. This patch ensures that the

`deflink` structure is correctly linked to the `sta` context, preventing the

null pointer dereference.

BUG: kernel NULL pointer dereference, address: 0000000000000400

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not-present page

PGD 0 P4D 0

Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI

CPU: 0 UID: 0 PID: 470 Comm: mt76-usb-rx phy Not tainted 6.12.13-gentoo-dist #1

Hardware name: /AMD HUDSON-M1, BIOS 4.6.4 11/15/2011

RIP: 0010:mt792x_rx_get_wcid+0x48/0x140 [mt792x_lib]

RSP: 0018:ffffa147c055fd98 EFLAGS: 00010202

RAX: 0000000000000000 RBX: ffff8e9ecb652000 RCX: 0000000000000000

RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8e9ecb652000

RBP: 0000000000000685 R08: ffff8e9ec6570000 R09: 0000000000000000

R10: ffff8e9ecd2ca000 R11: ffff8e9f22a217c0 R12: 0000000038010119

R13: 0000000080843801 R14: ffff8e9ec6570000 R15: ffff8e9ecb652000

FS: 0000000000000000(0000) GS:ffff8e9f22a00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000400 CR3: 000000000d2ea000 CR4: 00000000000006f0

Call Trace:

<TASK>

? __die_body.cold+0x19/0x27

? page_fault_oops+0x15a/0x2f0

? search_module_extables+0x19/0x60

? search_bpf_extables+0x5f/0x80

? exc_page_fault+0x7e/0x180

? asm_exc_page_fault+0x26/0x30

? mt792x_rx_get_wcid+0x48/0x140 [mt792x_lib]

mt7921_queue_rx_skb+0x1c6/0xaa0 [mt7921_common]

mt76u_alloc_queues+0x784/0x810 [mt76_usb]

? __pfx___mt76_worker_fn+0x10/0x10 [mt76]

__mt76_worker_fn+0x4f/0x80 [mt76]

kthread+0xd2/0x100

? __pfx_kthread+0x10/0x10

ret_from_fork+0x34/0x50

? __pfx_kthread+0x10/0x10

ret_from_fork_asm+0x1a/0x30

</TASK>

---[ end trace 0000000000000000 ]---