bsg incorrectly returns sg's masked_status value for device_status.

[jejb: fix up expression logic]
Reported-by: NDouglas Gilbert <dgilbert@interlog.com>
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>