can: j1939: j1939_sk_bind(): take priv after lock is held

syzbot reproduced following crash:

===============================================================================
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9844 Comm: syz-executor.0 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:__lock_acquire+0x1254/0x4a00 kernel/locking/lockdep.c:3828
Code: 00 0f 85 96 24 00 00 48 81 c4 f0 00 00 00 5b 41 5c 41 5d 41 5e 41
5f 5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02
00 0f 85 0b 28 00 00 49 81 3e 20 19 78 8a 0f 84 5f ee ff
RSP: 0018:ffff888099c3fb48 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000218 RSI: 0000000000000000 RDI: 0000000000000001
RBP: ffff888099c3fc60 R08: 0000000000000001 R09: 0000000000000001
R10: fffffbfff146e1d...