scsi: smartpqi: correct hang when deleting 32 lds

When each ld is deleted, a rescan event is triggered in the driver. These
can stack up waiting on mutex_lock.

Change to mutex_try_lock and schedule a rescan for later.

Reviewed-by: Scott Benesh <scott.benesh@microsemi.com>
Reviewed-by: Kevin Barnett <kevin.barnett@microsemi.com>
Signed-off-by: Mahesh Rajashekhara <mahesh.rajashekhara@microsemi.com>
Signed-off-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>