[PATCH] ppc32: fix dma_map_page() to use page_to_bus()

The following trivial patch changes dma_map_page() to use page_to_bus()
instead of open-coding it (incorrectly in some cases).
Signed-off-by: Eugene Surovegin <ebs@ebshome.net>
Signed-off-by: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-ppc/dma-mapping.h

@@ -117,7 +117,7 @@ dma_map_page(struct device *dev, struct page *page,
 
 	__dma_sync_page(page, offset, size, direction);
 
-	return (page - mem_map) * PAGE_SIZE + PCI_DRAM_OFFSET + offset;
+	return page_to_bus(page) + offset;
 }
 
 /* We do nothing. */