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/mtdblock_ro.c b/drivers/mtd/mtdblock_ro.c
index f5737b1..92759a9 100644
--- a/drivers/mtd/mtdblock_ro.c
+++ b/drivers/mtd/mtdblock_ro.c
@@ -40,7 +40,7 @@
 {
 	size_t retlen;
 
-	if (dev->mtd->write(dev->mtd, (block * 512), 512, &retlen, buf))
+	if (mtd_write(dev->mtd, (block * 512), 512, &retlen, buf))
 		return 1;
 	return 0;
 }