staging: mt29f_spinand: make use of mtd_to_nand()

mtd_to_nand() was recently introduced to avoid direct accesses to the
mtd->priv field. Use it where appropriate.
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>

drivers/staging/mt29f_spinand/mt29f_spinand.c

@@ -31,7 +31,7 @@
 
 static inline struct spinand_state *mtd_to_state(struct mtd_info *mtd)
 {
-	struct nand_chip *chip = (struct nand_chip *)mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 	struct spinand_info *info = (struct spinand_info *)chip->priv;
 	struct spinand_state *state = (struct spinand_state *)info->priv;
 
@@ -744,7 +744,7 @@ static void spinand_reset(struct spi_device *spi_nand)
 static void spinand_cmdfunc(struct mtd_info *mtd, unsigned int command,
 			    int column, int page)
 {
-	struct nand_chip *chip = (struct nand_chip *)mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 	struct spinand_info *info = (struct spinand_info *)chip->priv;
 	struct spinand_state *state = (struct spinand_state *)info->priv;