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/mtdchar.c b/drivers/mtd/mtdchar.c
index c7f4846..922da31 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -331,7 +331,7 @@
 		}
 
 		default:
-			ret = (*(mtd->write))(mtd, *ppos, len, &retlen, kbuf);
+			ret = mtd_write(mtd, *ppos, len, &retlen, kbuf);
 		}
 		if (!ret) {
 			*ppos += retlen;