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/orion_nand.c b/drivers/mtd/nand/orion_nand.c
index 5c21416..4ed4f67 100644
--- a/drivers/mtd/nand/orion_nand.c
+++ b/drivers/mtd/nand/orion_nand.c
@@ -25,7 +25,7 @@
 
 static void orion_nand_cmd_ctrl(struct mtd_info *mtd, int cmd, unsigned int ctrl)
 {
-	struct nand_chip *nc = mtd->priv;
+	struct nand_chip *nc = mtd_to_nand(mtd);
 	struct orion_nand_data *board = nc->priv;
 	u32 offs;
 
@@ -47,7 +47,7 @@
 
 static void orion_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
 {
-	struct nand_chip *chip = mtd->priv;
+	struct nand_chip *chip = mtd_to_nand(mtd);
 	void __iomem *io_base = chip->IO_ADDR_R;
 	uint64_t *buf64;
 	int i = 0;