scsi: smartpqi: Add controller cache flush during rmmod

Add in a call to flush the controller cache during driver removal.

Reviewed-by: Scott Benesh <scott.benesh@microchip.com>
Reviewed-by: Mike Mcgowan <mike.mcgowan@microchip.com>
Reviewed-by: Kevin Barnett <kevin.barnett@microchip.com>
Signed-off-by: Gilbert Wu <Gilbert.Wu@microchip.com>
Signed-off-by: Don Brace <don.brace@microchip.com>
Link: https://lore.kernel.org/r/166793532388.322537.878022136408270892.stgit@brunhilda


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>