libmsc/update_db_revision_3(): free memleaking db result

Found by ASAN

Change-Id: I2680c60e26b9876b428d4b75323f884f9ecd95b3

openbsc/src/libmsc/db.c

@@ -346,6 +346,8 @@ static int update_db_revision_3(void)
 		LOGP(DDB, LOGL_ERROR,
 			"Failed to commit the transaction (upgrade from rev 3)\n");
 		return -EINVAL;
+	} else {
+		dbi_result_free(result);
 	}
 
 	/* Shrink DB file size by actually wiping out SMS_3 table data */