db: Avoid use uninitialized rc if running 0 statements

Caught by new gcc 11.1.0:
/git/osmo-hlr/src/db.c:257:16: error: ‘rc’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  257 |         return rc;
      |                ^~

Change-Id: I45e1fede234cd4446a7061fb908bf344eee72f5a

src/db.c

@@ -234,7 +234,7 @@ void db_close(struct db_context *dbc)
 
 static int db_run_statements(struct db_context *dbc, const char **statements, size_t statements_count)
 {
-	int rc;
+	int rc = 0;
 	int i;
 	for (i = 0; i < statements_count; i++) {
 		const char *stmt_str = statements[i];