[SCSI] fix scsi_wait_scan

Commit  c7510859
Author: Rafael J. Wysocki <rjw@sisk.pl>
Date:   Sun Apr 12 20:06:56 2009 +0200

    PM/Hibernate: Wait for SCSI devices scan to complete during resume

Broke the scsi_wait_scan module in 2.6.30.  Apparently debian still uses it so
fix it and backport to stable before removing it in 3.6.

The breakage is caused because the function template in
include/scsi/scsi_scan.h is defined to be a nop unless SCSI is built in.
That means that in the modular case (which is every distro), the
scsi_wait_scan module does a simple async_synchronize_full() instead of
waiting for scans.

Cc: <stable@vger.kernel.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>