{src,util}: Use NULL instead of 0 for pointer

Change-Id: I75fa4577055f25dde0a8b1044c005bba72cabd92
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/26857
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/vgabios/testbios.c

@@ -135,8 +135,8 @@ biosemu(u8 *biosmem, u32 biosmem_size, struct device * dev, unsigned long
 int main(int argc, char **argv)
 {
 	int ret;
-	char *absegname = 0;
-	void *abseg = 0;
+	char *absegname = NULL;
+	void *abseg = NULL;
 	int c, trace = 0;
 	unsigned char *cp;
 	char *filename;