ARM: 9218/1: dma-mapping: fix pointer/integer warning

Fix the use of a pointer assignment from integer where false
is being used instead of NULL. Fix the following warning by
usign NULL:

arch/arm/mm/dma-mapping.c:712:52: warning: Using plain integer as NULL pointer
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

arch/arm/mm/dma-mapping.c

@@ -709,7 +709,7 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 
 	*handle = DMA_MAPPING_ERROR;
 	allowblock = gfpflags_allow_blocking(gfp);
-	cma = allowblock ? dev_get_cma_area(dev) : false;
+	cma = allowblock ? dev_get_cma_area(dev) : NULL;
 
 	if (cma)
 		buf->allocator = &cma_allocator;