[SERIAL] 8250_early.c passing 0 instead of NULL

Fix sparse warning about passing `0` to  simple_strtoul()

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/serial/8250_early.c b/drivers/serial/8250_early.c
index b7a5dd7..59ba5d9 100644
--- a/drivers/serial/8250_early.c
+++ b/drivers/serial/8250_early.c
@@ -164,7 +164,7 @@
 
 	if ((options = strchr(options, ','))) {
 		options++;
-		device->baud = simple_strtoul(options, 0, 0);
+		device->baud = simple_strtoul(options, NULL, 0);
 		length = min(strcspn(options, " "), sizeof(device->options));
 		strncpy(device->options, options, length);
 	} else {