ARM: 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 ARM specific implementations to use this
helper.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
diff --git a/arch/arm/mach-ixp4xx/ixdp425-setup.c b/arch/arm/mach-ixp4xx/ixdp425-setup.c
index e7b8bef..333b0f9 100644
--- a/arch/arm/mach-ixp4xx/ixdp425-setup.c
+++ b/arch/arm/mach-ixp4xx/ixdp425-setup.c
@@ -76,7 +76,7 @@
 static void
 ixdp425_flash_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);
 	int offset = (int)this->priv;
 
 	if (ctrl & NAND_CTRL_CHANGE) {