mtd: introduce mtd_sync 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 86308ac..b5722ec 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -155,7 +155,7 @@
 
 	/* Only sync if opened RW */
 	if ((file->f_mode & FMODE_WRITE) && mtd->sync)
-		mtd->sync(mtd);
+		mtd_sync(mtd);
 
 	iput(mfi->ino);