mtd: nand: update mtd_to_nand()

Now that all drivers are using the mtd instance embedded in the nand_chip
struct we can safely update the mtd_to_nand() implementation to use
the container_of macro instead of returning the content of mtd->priv.
This will allow us to remove mtd->priv = chip assignments done in all
NAND controller drivers.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

include/linux/mtd/nand.h

@@ -734,7 +734,7 @@ static inline struct device_node *nand_get_flash_node(struct nand_chip *chip)
 
 static inline struct nand_chip *mtd_to_nand(struct mtd_info *mtd)
 {
-	return mtd->priv;
+	return container_of(mtd, struct nand_chip, mtd);
 }
 
 static inline struct mtd_info *nand_to_mtd(struct nand_chip *chip)