mtd: nand: Patch remaining places where nand_to_mtd() should be used

Some drivers are still directly accessing the chip->mtd field. Patch
them to use nand_to_mtd() instead.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
diff --git a/drivers/mtd/nand/mxs_nand_spl.c b/drivers/mtd/nand/mxs_nand_spl.c
index a8a3084..ff28df4 100644
--- a/drivers/mtd/nand/mxs_nand_spl.c
+++ b/drivers/mtd/nand/mxs_nand_spl.c
@@ -147,7 +147,7 @@
 
 	/* init mxs nand driver */
 	board_nand_init(&nand_chip);
-	mtd = &nand_chip.mtd;
+	mtd = nand_to_mtd(&nand_chip);
 	/* set mtd functions */
 	nand_chip.cmdfunc = mxs_nand_command;
 	nand_chip.numchips = 1;