mtd: partitions: redboot: seek fis-index-block in the right node

fis-index-block is seeked in the master node and not in the partitions node.
For following binding and current usage, the driver need to check the
partitions subnode.

Fixes: c0e118c8 ("mtd: partitions: Add OF support to RedBoot partitions")
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210520114851.1274609-1-clabbe@baylibre.com

drivers/mtd/parsers/redboot.c

@@ -45,6 +45,7 @@ static inline int redboot_checksum(struct fis_image_desc *img)
 static void parse_redboot_of(struct mtd_info *master)
 {
 	struct device_node *np;
+	struct device_node *npart;
 	u32 dirblock;
 	int ret;
 
@@ -52,7 +53,11 @@ static void parse_redboot_of(struct mtd_info *master)
 	if (!np)
 		return;
 
-	ret = of_property_read_u32(np, "fis-index-block", &dirblock);
+	npart = of_get_child_by_name(np, "partitions");
+	if (!npart)
+		return;
+
+	ret = of_property_read_u32(npart, "fis-index-block", &dirblock);
 	if (ret)
 		return;