ARM: dmabounce: check pointer against NULL not 0

Pointers should be checked against NULL rather than 0, otherwise we
get sparse warnings.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/common/dmabounce.c b/arch/arm/common/dmabounce.c
index 0077c1b..b4a8759 100644
--- a/arch/arm/common/dmabounce.c
+++ b/arch/arm/common/dmabounce.c
@@ -249,7 +249,7 @@
 		DO_STATS ( device_info->map_op_count++ );
 
 	buf = alloc_safe_buffer(device_info, ptr, size, dir);
-	if (buf == 0) {
+	if (buf == NULL) {
 		dev_err(dev, "%s: unable to map unsafe buffer %p!\n",
 		       __func__, ptr);
 		return ~0;