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/mtdswap.c b/drivers/mtd/mtdswap.c
index 8579739..cb794e7 100644
--- a/drivers/mtd/mtdswap.c
+++ b/drivers/mtd/mtdswap.c
@@ -1048,7 +1048,7 @@
 	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);
 
 	if (d->mtd->sync)
-		d->mtd->sync(d->mtd);
+		mtd_sync(d->mtd);
 	return 0;
 }