f2fs: compress: remove unneed check condition

In only call path of __cluster_may_compress(), __f2fs_write_data_pages()
has checked SBI_POR_DOING condition, and also cluster_may_compress()
has checked CP_ERROR_FLAG condition, so remove redundant check condition
in __cluster_may_compress() for cleanup.

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