[SCSI] scsi_queue_work() documented return value is incorrect

If you examine the queue_work() routine you'll see that it returns
1 on success, 0 if the work is already queued.

This patch corrects the source code documentation for the
scsi_queue_work function.

Signed-off-by: Michael Reed <mdr@sgi.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>