MIPS: Don't unmap the memory for dma_sync*.

We were getting away with this for so long only because the only platform
with a non-empty plat_unmap_dma_mem() doesn't call dma_sync_sg_for_cpu()
and dma_sync_sg_for_device() from its commonly used drivers.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/dma-default.c

@@ -324,7 +324,6 @@ void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
 		if (cpu_is_noncoherent_r10000(dev))
 			__dma_sync((unsigned long)page_address(sg_page(sg)),
 			           sg->length, direction);
-		plat_unmap_dma_mem(sg->dma_address);
 	}
 }
 
@@ -342,7 +341,6 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nele
 		if (!plat_device_is_coherent(dev))
 			__dma_sync((unsigned long)page_address(sg_page(sg)),
 			           sg->length, direction);
-		plat_unmap_dma_mem(sg->dma_address);
 	}
 }