scsi: ufs: Improve interrupt handling for shared interrupts

[ Upstream commit 127d5f7c4b653b8be5eb3b2c7bbe13728f9003ff ]

For shared interrupts, the interrupt status might be zero, so check that
first.

Link: https://lore.kernel.org/r/20200811133936.19171-2-adrian.hunter@intel.com


Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>