mtd: introduce mtd_write 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/mtdpart.c b/drivers/mtd/mtdpart.c
index 59cd797..96574a0 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -188,8 +188,7 @@
 		len = 0;
 	else if (to + len > mtd->size)
 		len = mtd->size - to;
-	return part->master->write(part->master, to + part->offset,
-				    len, retlen, buf);
+	return mtd_write(part->master, to + part->offset, len, retlen, buf);
 }
 
 static int part_panic_write(struct mtd_info *mtd, loff_t to, size_t len,