f2fs: use correct errno

This patch is to fix misused error number.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 57a5f7b..47fbb72 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -505,7 +505,7 @@
 
 bool discard_next_dnode(struct f2fs_sb_info *sbi, block_t blkaddr)
 {
-	int err = -ENOTSUPP;
+	int err = -EOPNOTSUPP;
 
 	if (test_opt(sbi, DISCARD)) {
 		struct seg_entry *se = get_seg_entry(sbi,