pinctrl: generic: scan for "pins" and "groups" properties in sub-nodes

In cases where the pins and groups definitions are in a sub-node, as:

	uart_a {
		mux {
			groups = "uart_tx_a", "uart_rx_a";
			function = "uart_a";
		};
	};

pinctrl_generic_set_state_subnode() returns an error for the top-level
node and pinctrl_generic_set_state() fails. Instead, return success so
that the child nodes are tried.
Signed-off-by: NBeniamino Galvani <b.galvani@gmail.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

drivers/pinctrl/pinctrl-generic.c

@@ -312,8 +312,10 @@ static int pinctrl_generic_set_state_subnode(struct udevice *dev,
 		is_group = true;
 		strings_count = fdt_count_strings(fdt, node,
 						  subnode_target_type);
-		if (strings_count < 0)
-			return -EINVAL;
+		if (strings_count < 0) {
+			/* skip this node; may contain config child nodes */
+			return 0;
+		}
 	}
 
 	for (i = 0; i < strings_count; i++) {