Staging: most: mostcore/core.c. Fix "Using plain integer as NULL pointer" warnings

This patch fixes the warning generated by sparse: "Using plain integer
as NULL pointer" by replacing the pointer test against 0 with a logical test.
Signed-off-by: NAdrian Remonda <adrianremonda@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/most/mostcore/core.c

@@ -982,7 +982,7 @@ static ssize_t store_add_link(struct most_aim_obj *aim_obj,
 	if (ret)
 		return ret;
 
-	if (mdev_devnod == 0 || *mdev_devnod == 0) {
+	if (!mdev_devnod || *mdev_devnod == 0) {
 		snprintf(devnod_buf, sizeof(devnod_buf), "%s-%s", mdev, mdev_ch);
 		mdev_devnod = devnod_buf;
 	}