[SCSI] don't reap targets upon device_add failure

This patch (as1358) fixes a bug in the error pathway of
scsi_target_add().  If registration fails, the target should not be
reaped.  The reaping occurs later, when scanning is finished and all
the child devices are removed.  The current code leaves an unbalanced
value in starget->reap_ref.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>