f2fs: remove unneeded parameter of change_curseg

allocate_segment_by_default is the only caller of change_curseg passing
@reuse with 'false', but commit 763bfe1b ("f2fs: remove reusing any
prefree segments") removes the calling, after that, @reuse in
change_curseg always be true, so, let's clean up the unneeded parameter.

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