scsi: pm80xx: Corrected dma_unmap_sg() parameter

[ Upstream commit 76cb25b058034d37244be6aca97a2ad52a5fbcad ]

For the function dma_unmap_sg(), the <nents> parameter should be number of
elements in the scatter list prior to the mapping, not after the mapping.

Signed-off-by: Deepak Ukey <deepak.ukey@microchip.com>
Signed-off-by: Viswas G <Viswas.G@microchip.com>
Acked-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>