Stanse found a potential NULL dereference in scsi_kill_request.

Instead of triggering BUG() in 'if (unlikely(cmd == NULL))' branch,
the kernel will Oops earlier on cmd dereference.

Move the dereferences after the if.
Signed-off-by: NJiri Slaby <jirislaby@gmail.com>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>