dma-mapping: remove an incorrect __iommem annotation

memmap return a regular void pointer, not and __iomem one.
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/coherent.c

@@ -43,7 +43,7 @@ static int dma_init_coherent_memory(
 	struct dma_coherent_mem **mem)
 {
 	struct dma_coherent_mem *dma_mem = NULL;
-	void __iomem *mem_base = NULL;
+	void *mem_base = NULL;
 	int pages = size >> PAGE_SHIFT;
 	int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
 	int ret;