xtensa: dma-mapping.h is using linux/scatterlist.h functions, so include it

It's currently using asm/scatterlist.h, but that is not enough.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/asm-xtensa/dma-mapping.h

@@ -11,10 +11,10 @@
 #ifndef _XTENSA_DMA_MAPPING_H
 #define _XTENSA_DMA_MAPPING_H
 
-#include <asm/scatterlist.h>
 #include <asm/cache.h>
 #include <asm/io.h>
 #include <linux/mm.h>
+#include <linux/scatterlist.h>
 
 /*
  * DMA-consistent mapping functions.