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/mtdchar.c b/drivers/mtd/mtdchar.c
index e74f570..234e3d2 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -325,7 +325,7 @@
 			ops.ooboffs = 0;
 			ops.len = len;
 
-			ret = mtd->write_oob(mtd, *ppos, &ops);
+			ret = mtd_write_oob(mtd, *ppos, &ops);
 			retlen = ops.retlen;
 			break;
 		}
@@ -426,7 +426,7 @@
 		return PTR_ERR(ops.oobbuf);
 
 	start &= ~((uint64_t)mtd->writesize - 1);
-	ret = mtd->write_oob(mtd, start, &ops);
+	ret = mtd_write_oob(mtd, start, &ops);
 
 	if (ops.oobretlen > 0xFFFFFFFFU)
 		ret = -EOVERFLOW;
@@ -609,7 +609,7 @@
 		ops.oobbuf = NULL;
 	}
 
-	ret = mtd->write_oob(mtd, (loff_t)req.start, &ops);
+	ret = mtd_write_oob(mtd, (loff_t)req.start, &ops);
 
 	kfree(ops.datbuf);
 	kfree(ops.oobbuf);