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/sm_ftl.c b/drivers/mtd/sm_ftl.c
index 748aa44..4ec2af7 100644
--- a/drivers/mtd/sm_ftl.c
+++ b/drivers/mtd/sm_ftl.c
@@ -343,7 +343,7 @@
 	ops.ooblen = SM_OOB_SIZE;
 	ops.oobbuf = (void *)oob;
 
-	ret = mtd->write_oob(mtd, sm_mkoffset(ftl, zone, block, boffset), &ops);
+	ret = mtd_write_oob(mtd, sm_mkoffset(ftl, zone, block, boffset), &ops);
 
 	/* Now we assume that hardware will catch write bitflip errors */
 	/* If you are paranoid, use CONFIG_MTD_NAND_VERIFY_WRITE */