net/smc: do not leave a dangling sk pointer in __smc_create()

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

net/smc: do not leave a dangling sk pointer in __smc_create()

Thanks to commit 4bbd360a5084 ("socket: Print pf->create() when
it does not clear sock->sk on failure."), syzbot found an issue with AF_SMC:

smc_create must clear sock->sk on failure, family: 43, type: 1, protocol: 0
WARNING: CPU: 0 PID: 5827 at net/socket.c:1565 __sock_create+0x96f/0xa30 net/socket.c:1563
Modules linked in:
CPU: 0 UID: 0 PID: 5827 Comm: syz-executor259 Not tainted 6.12.0-rc6-next-20241106-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:__sock_create+0x96f/0xa30 net/socket.c:1563
Code: 03 00 74 08 4c 89 e7 e8 4f 3b 85 f8 49 8b 34 24 48 c7 c7 40 89 0c 8d 8b 54 24 04 8b 4c 24 0c 44 8b 44 24 08 e8 32 78 db f7 90 <0f> 0b 90 90 e9 d3 fd ff ff 89 e9 80 e1 07 fe c1 38 c1 0f 8c ee f7
RSP: 0018:ffffc90003e4fda0 EFLAGS: 00010246
RAX: 099c6f938c7f4700 RBX: 1ffffffff1a595fd RCX: ffff888034823c00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000ffffffe9 R08: ffffffff81567052 R09: 1ffff920007c9f50
R10: dffffc0000000000 R11: fffff520007c9f51 R12: ffffffff8d2cafe8
R13: 1ffffffff1a595fe R14: ffffffff9a789c40 R15: ffff8880764298c0
FS: 000055557b518380(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa62ff43225 CR3: 0000000031628000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
sock_create net/socket.c:1616 [inline]
__sys_socket_create net/socket.c:1653 [inline]
__sys_socket+0x150/0x3c0 net/socket.c:1700
__do_sys_socket net/socket.c:1714 [inline]
__se_sys_socket net/socket.c:1712 [inline]

For reference, see commit 2d859aff775d ("Merge branch
'do-not-leave-dangling-sk-pointers-in-pf-create-functions'")