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/fs/logfs/dev_mtd.c b/fs/logfs/dev_mtd.c
index 136c736..3f465882 100644
--- a/fs/logfs/dev_mtd.c
+++ b/fs/logfs/dev_mtd.c
@@ -119,8 +119,7 @@
 {
 	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
 
-	if (mtd->sync)
-		mtd_sync(mtd);
+	mtd_sync(mtd);
 }
 
 static int logfs_mtd_readpage(void *_sb, struct page *page)