Move as much as possible outside the critical section in queuecommand, eg:
 - Set the scsi_done field before acquiring the lock
 - Call asc_scsi_done after dropping the lock

Also remove a comment suggesting we should enable interrupts (now we do)
and do some minor reformatting for readability.
Signed-off-by: NMatthew Wilcox <matthew@wil.cx>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>