mtd: nand: add nand_to_mtd() helper

Add a new helper to retrieve the MTD device attached to a NAND chip.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

include/linux/mtd/nand.h

@@ -737,6 +737,11 @@ static inline struct nand_chip *mtd_to_nand(struct mtd_info *mtd)
 	return mtd->priv;
 }
 
+static inline struct mtd_info *nand_to_mtd(struct nand_chip *chip)
+{
+	return &chip->mtd;
+}
+
 /*
  * NAND Flash Manufacturer ID Codes
  */