sparc/iommu: use sbus_iommu_unmap_page in sbus_iommu_unmap_sg

Use the page-level helper instead of duplicating the logic, while also
fixing the incorrect handling of larger than page sized offsets in
the sg variant.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/mm/iommu.c

@@ -321,11 +321,11 @@ static void sbus_iommu_unmap_sg(struct device *dev, struct scatterlist *sgl,
 		int nents, enum dma_data_direction dir, unsigned long attrs)
 {
 	struct scatterlist *sg;
-	int i, n;
+	int i;
 
 	for_each_sg(sgl, sg, nents, i) {
-		n = (sg->length + sg->offset + PAGE_SIZE-1) >> PAGE_SHIFT;
-		iommu_release_one(dev, sg->dma_address & PAGE_MASK, n);
+		sbus_iommu_unmap_page(dev, sg->dma_address, sg->length, dir,
+				attrs);
 		sg->dma_address = 0x21212121;
 	}
 }