mtd: fix 'part' field data corruption in mtd_info

Commit 46b5889c ("mtd: implement proper partition handling")
started using "mtd_get_master_ofs()" in mtd callbacks to determine
memory offsets by means of 'part' field from mtd_info, what previously
was smashed accessing 'master' field in the mtd_set_dev_defaults() method.
That provides wrong offset what causes hardware access errors.

Just make 'part', 'master' as separate fields, rather than using
union type to avoid 'part' data corruption when mtd_set_dev_defaults()
is called.

Fixes: 46b5889c ("mtd: implement proper partition handling")
Signed-off-by: Oleksandr Ocheretnyi <oocheret@cisco.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220417184649.449289-1-oocheret@cisco.com

include/linux/mtd/mtd.h

@@ -389,10 +389,8 @@ struct mtd_info {
 	/* List of partitions attached to this MTD device */
 	struct list_head partitions;
 
-	union {
-		struct mtd_part part;
-		struct mtd_master master;
-	};
+	struct mtd_part part;
+	struct mtd_master master;
 };
 
 static inline struct mtd_info *mtd_get_master(struct mtd_info *mtd)