mtd: introduce mtd_write_oob interface

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
index fcab50e..20a112f 100644
--- a/drivers/mtd/nand/nand_bbt.c
+++ b/drivers/mtd/nand/nand_bbt.c
@@ -350,7 +350,7 @@
 	ops.oobbuf = oob;
 	ops.len = len;
 
-	return mtd->write_oob(mtd, offs, &ops);
+	return mtd_write_oob(mtd, offs, &ops);
 }
 
 static u32 bbt_get_ver_offs(struct mtd_info *mtd, struct nand_bbt_descr *td)