f2fs: give RO message when recovering superblock

When one of superblocks is missing, f2fs recovers it with the valid one.
But, even if f2fs is mounted as RO, we'd better notify that too.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1298,6 +1298,9 @@ int f2fs_commit_super(struct f2fs_sb_info *sbi, bool recover)
 	struct buffer_head *bh;
 	int err;
 
+	if (f2fs_readonly(sbi->sb) || bdev_read_only(sbi->sb->s_bdev))
+		return -EROFS;
+
 	/* write back-up superblock first */
 	bh = sb_getblk(sbi->sb, sbi->valid_super_block ? 0: 1);
 	if (!bh)
@@ -1565,7 +1568,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	kfree(options);
 
 	/* recover broken superblock */
-	if (recovery && !f2fs_readonly(sb) && !bdev_read_only(sb->s_bdev)) {
+	if (recovery) {
 		err = f2fs_commit_super(sbi, true);
 		f2fs_msg(sb, KERN_INFO,
 			"Try to recover %dth superblock, ret: %ld",