This patch changes the way we complete commands.  In the old method when we
got a completion we searched our command list from the top until we find it.

This method uses a tag associated with each command (not SCSI command tagging)
to index us directly to the completed command.  This helps performance.
Signed-off-by: NDon Brace <dab@hp.com>
Signed-off-by: NMike Miller <mike.miller@hp.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>