f2fs: remove repeated f2fs_bug_on which has already existed
      in function invalidate_blocks.
Signed-off-by: NZhikang Zhang <zhangzhikang1@huawei.com>
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>