Fix SCSI generic read() incorrectly returning success after detecting an
error.

Cc: <stable@vger.kernel.org>
Signed-off-by: NTony Battersby <tonyb@cybernetics.com>
Acked-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>