sbp2_command_orb_lock must be held when accessing the _orb_inuse list.

Fixes an oops in sbp2util_find_command_for_SCpnt after sbp2scsi_abort:
https://bugzilla.novell.com/show_bug.cgi?id=113734



Signed-off-by: Jody McIntyre <scjody@steamballoon.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>