blackfin: nand: make use of mtd_to_nand() where appropriate

mtd_to_nand() was recently introduced to avoid direct accesses to the
mtd->priv field. Update all blackfin specific implementations to use
this helper.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

arch/blackfin/mach-bf537/boards/stamp.c

@@ -404,7 +404,7 @@ static struct mtd_partition bfin_plat_nand_partitions[] = {
 #define BFIN_NAND_PLAT_ALE 1
 static void bfin_plat_nand_cmd_ctrl(struct mtd_info *mtd, int cmd, unsigned int ctrl)
 {
-	struct nand_chip *this = mtd->priv;
+	struct nand_chip *this = mtd_to_nand(mtd);
 
 	if (cmd == NAND_CMD_NONE)
 		return;

arch/blackfin/mach-bf561/boards/acvilon.c

@@ -267,7 +267,7 @@ static struct mtd_partition bfin_plat_nand_partitions[] = {
 static void bfin_plat_nand_cmd_ctrl(struct mtd_info *mtd, int cmd,
 				    unsigned int ctrl)
 {
-	struct nand_chip *this = mtd->priv;
+	struct nand_chip *this = mtd_to_nand(mtd);
 
 	if (cmd == NAND_CMD_NONE)
 		return;