f2fs: skip adding a discard command if exists

When recovering zoned UFS, sometimes we add the same zone to discard multiple
times. Simple workaround is to bypass adding it.
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -1380,7 +1380,8 @@ static void __insert_discard_cmd(struct f2fs_sb_info *sbi,
 			p = &(*p)->rb_right;
 			leftmost = false;
 		} else {
-			f2fs_bug_on(sbi, 1);
+			/* Let's skip to add, if exists */
+			return;
 		}
 	}