scsi: mpt3sas: Add an I/O barrier

A barrier should be added to ensure proper ordering of memory mapped
writes.
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Chaitra P B <chaitra.basappa@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_base.c

@@ -3344,6 +3344,7 @@ _base_mpi_ep_writeq(__u64 b, volatile void __iomem *addr,
 	spin_lock_irqsave(writeq_lock, flags);
 	writel((u32)(data_out), addr);
 	writel((u32)(data_out >> 32), (addr + 4));
+	mmiowb();
 	spin_unlock_irqrestore(writeq_lock, flags);
 }