mtd: nand: make use of mtd_to_nand() in NAND drivers

mtd_to_nand() was recently introduced to avoid direct accesses to the
mtd->priv field. Update all NAND drivers to use it.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
diff --git a/drivers/mtd/nand/fsl_upm.c b/drivers/mtd/nand/fsl_upm.c
index b3f4a01..68ec128 100644
--- a/drivers/mtd/nand/fsl_upm.c
+++ b/drivers/mtd/nand/fsl_upm.c
@@ -79,7 +79,7 @@
 
 static void fun_cmd_ctrl(struct mtd_info *mtd, int cmd, unsigned int ctrl)
 {
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 	struct fsl_upm_nand *fun = to_fsl_upm_nand(mtd);
 	u32 mar;
 
@@ -109,7 +109,7 @@
 
 static void fun_select_chip(struct mtd_info *mtd, int mchip_nr)
 {
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 	struct fsl_upm_nand *fun = to_fsl_upm_nand(mtd);
 
 	if (mchip_nr == -1) {