arch/arm/xen: Remove duplicate header

Remove duplicate header which is included twice.
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/arm/xen/mm.c

@@ -7,7 +7,6 @@
 #include <linux/of_address.h>
 #include <linux/slab.h>
 #include <linux/types.h>
-#include <linux/dma-mapping.h>
 #include <linux/vmalloc.h>
 #include <linux/swiotlb.h>