scsi: sd: Introduce a new local variable in sd_check_events()

Instead of using 'retval' to represent first a SCSI status and later
whether or not a disk change event occurred, introduce a new variable for
the latter purpose.

Link: https://lore.kernel.org/r/20210415220826.29438-17-bvanassche@acm.org


Cc: Christoph Hellwig <hch@lst.de>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>