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>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 006f87d..ffe4616 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1298,6 +1298,9 @@
 	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 @@
 	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",