f2fs: correct return value of f2fs_trim_fs

Correct return value in two cases:
- return EINVAL if end boundary is out-of-range.
- return EIO if fs needs off-line check.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>