scsi: megaraid_mbox: remove bogus use of pci_dma_sync_sg_* APIs

The dma_map_sg / dma_unmap_sg APIs called from scsi_dma_map /
scsi_dma_unmap already transfer memory ownership to the device or cpu
respectively.  Adding additional calls to pci_dma_sync_sg_* will in fact
lead to data corruption if we end up using swiotlb for some reason.

Also remove the now pointless megaraid_mbox_sync_scb function.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>