scsi: pmcraid: Use sgl_alloc_order() and sgl_free_order()

Use the sgl_alloc_order() and sgl_free_order() functions instead of open
coding these functions.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Cc: Anil Ravindranath <anil_ravindranath@pmc-sierra.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>