xtensa: use for_each_sg()

This replaces the plain loop over the sglist array with for_each_sg()
macro which consists of sg_next() function calls.  Since xtensa doesn't
select ARCH_HAS_SG_CHAIN, it is not necessary to use for_each_sg() in
order to loop over each sg element.  But this can help find problems
with drivers that do not properly initialize their sg tables when
CONFIG_DEBUG_SG is enabled.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/xtensa/include/asm/dma-mapping.h

@@ -52,14 +52,15 @@ dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
 }
 
 static inline int
-dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+dma_map_sg(struct device *dev, struct scatterlist *sglist, int nents,
 	   enum dma_data_direction direction)
 {
 	int i;
+	struct scatterlist *sg;
 
 	BUG_ON(direction == DMA_NONE);
 
-	for (i = 0; i < nents; i++, sg++ ) {
+	for_each_sg(sglist, sg, nents, i) {
 		BUG_ON(!sg_page(sg));
 
 		sg->dma_address = sg_phys(sg);
@@ -124,20 +125,24 @@ dma_sync_single_range_for_device(struct device *dev, dma_addr_t dma_handle,
 	consistent_sync((void *)bus_to_virt(dma_handle)+offset,size,direction);
 }
 static inline void
-dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
+dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sglist, int nelems,
 		 enum dma_data_direction dir)
 {
 	int i;
-	for (i = 0; i < nelems; i++, sg++)
+	struct scatterlist *sg;
+
+	for_each_sg(sglist, sg, nelems, i)
 		consistent_sync(sg_virt(sg), sg->length, dir);
 }
 
 static inline void
-dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
-		 enum dma_data_direction dir)
+dma_sync_sg_for_device(struct device *dev, struct scatterlist *sglist,
+		       int nelems, enum dma_data_direction dir)
 {
 	int i;
-	for (i = 0; i < nelems; i++, sg++)
+	struct scatterlist *sg;
+
+	for_each_sg(sglist, sg, nelems, i)
 		consistent_sync(sg_virt(sg), sg->length, dir);
 }
 static inline int