UBIFS: allow for sync_fs when read-only

sync_fs can be called even if the file system is mounted
read-only.  Ensure the commit is not run in that case.
Reported-by: Zoltan Sogor <weth@inf.u-szeged.hu>
Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>

fs/ubifs/super.c

@@ -420,14 +420,14 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 	int i, ret = 0, err;
 	long long bud_bytes;
 
-	if (c->jheads)
+	if (c->jheads) {
 		for (i = 0; i < c->jhead_cnt; i++) {
 			err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
 			if (err && !ret)
 				ret = err;
 		}
 
-	/* Commit the journal unless it has too few data */
+		/* Commit the journal unless it has too little data */
 		spin_lock(&c->buds_lock);
 		bud_bytes = c->bud_bytes;
 		spin_unlock(&c->buds_lock);
@@ -436,6 +436,7 @@ static int ubifs_sync_fs(struct super_block *sb, int wait)
 			if (err)
 				return err;
 		}
+	}
 
 	/*
 	 * We ought to call sync for c->ubi but it does not have one. If it had