mtd: do not use mtd->lock, unlock and is_locked directly

Instead, call the corresponding MTD API function which will return
'-EOPNOTSUPP' if the operation is not supported.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
index 9119f76..aaafb5e 100644
--- a/drivers/mtd/mtdconcat.c
+++ b/drivers/mtd/mtdconcat.c
@@ -555,12 +555,9 @@
 		else
 			size = len;
 
-		if (subdev->lock) {
-			err = mtd_lock(subdev, ofs, size);
-			if (err)
-				break;
-		} else
-			err = -EOPNOTSUPP;
+		err = mtd_lock(subdev, ofs, size);
+		if (err)
+			break;
 
 		len -= size;
 		if (len == 0)
@@ -595,12 +592,9 @@
 		else
 			size = len;
 
-		if (subdev->unlock) {
-			err = mtd_unlock(subdev, ofs, size);
-			if (err)
-				break;
-		} else
-			err = -EOPNOTSUPP;
+		err = mtd_unlock(subdev, ofs, size);
+		if (err)
+			break;
 
 		len -= size;
 		if (len == 0)