drivers: of: fix build break if asm/dma-contiguous.h is missing

It is not needed to include asm/dma-contiguous.h header to compile
reserved memory initialization code, so remove it to avoid build break
on architectures without CMA support.
Signed-off-by: NMarek Szyprowski <m.szyprowski@samsung.com>
Tested-by: NGuenter Roeck <linux@roeck-us.net>

drivers/of/of_reserved_mem.c

@@ -11,8 +11,6 @@
  * License or (at your optional) any later version of the license.
  */
 
-#include <asm/dma-contiguous.h>
-
 #include <linux/memblock.h>
 #include <linux/err.h>
 #include <linux/of.h>