mtd: do not use mtd->sync directly

This patch teaches 'mtd_sync()' to do nothing when the MTD driver does
not have the '->sync()' method, which allows us to remove all direct
'mtd->sync' accesses.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
index 9f265cc..9fdb353 100644
--- a/drivers/mtd/ubi/kapi.c
+++ b/drivers/mtd/ubi/kapi.c
@@ -714,9 +714,7 @@
 	if (!ubi)
 		return -ENODEV;
 
-	if (ubi->mtd->sync)
-		mtd_sync(ubi->mtd);
-
+	mtd_sync(ubi->mtd);
 	ubi_put_device(ubi);
 	return 0;
 }