convert swiotlb to use dma_get_mask

swiotlb can use dma_get_mask() instead of the homegrown function.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: tony.luck@intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/dma-mapping.h

@@ -65,7 +65,7 @@ static inline int is_buffer_dma_capable(u64 mask, dma_addr_t addr, size_t size)
 
 static inline u64 dma_get_mask(struct device *dev)
 {
-	if (dev->dma_mask && *dev->dma_mask)
+	if (dev && dev->dma_mask && *dev->dma_mask)
 		return *dev->dma_mask;
 	return DMA_32BIT_MASK;
 }

lib/swiotlb.c

@@ -276,11 +276,7 @@ swiotlb_late_init_with_default_size(size_t default_size)
 static int
 address_needs_mapping(struct device *hwdev, dma_addr_t addr, size_t size)
 {
-	dma_addr_t mask = 0xffffffff;
-	/* If the device has a mask, use it, otherwise default to 32 bits */
-	if (hwdev && hwdev->dma_mask)
-		mask = *hwdev->dma_mask;
-	return !is_buffer_dma_capable(mask, addr, size);
+	return !is_buffer_dma_capable(dma_get_mask(hwdev), addr, size);
 }
 
 static int is_swiotlb_buffer(char *addr)