mtd: parsers: ofpart: limit parsing of deprecated DT syntax

For backward compatibility ofpart still supports the old syntax like:
spi-flash@0 {
	compatible = "jedec,spi-nor";
	reg = <0x0>;

	partition@0 {
		label = "bootloader";
		reg = <0x0 0x100000>;
	};
};
(without "partitions" subnode).

There is no reason however to support nested partitions without a clear
"compatible" string like:
partitions {
	compatible = "fixed-partitions";
	#address-cells = <1>;
	#size-cells = <1>;

	partition@0 {
		label = "bootloader";
		reg = <0x0 0x100000>;

		partition@0 {
			label = "config";
			reg = <0x80000 0x80000>;
		};
	};
};
(we never officially supported or documented that).

Make sure ofpart doesn't attempt to parse above.

Cc: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210302190012.1255-1-zajec5@gmail.com

drivers/mtd/parsers/ofpart_core.c

@@ -53,7 +53,7 @@ static int parse_fixed_partitions(struct mtd_info *master,
 		return 0;
 
 	ofpart_node = of_get_child_by_name(mtd_node, "partitions");
-	if (!ofpart_node) {
+	if (!ofpart_node && !master->parent) {
 		/*
 		 * We might get here even when ofpart isn't used at all (e.g.,
 		 * when using another parser), so don't be louder than
@@ -64,6 +64,8 @@ static int parse_fixed_partitions(struct mtd_info *master,
 		ofpart_node = mtd_node;
 		dedicated = false;
 	}
+	if (!ofpart_node)
+		return 0;
 
 	of_id = of_match_node(parse_ofpart_match_table, ofpart_node);
 	if (dedicated && !of_id) {