f2fs: compress: fix to avoid memory leak on cc->cpages

Memory allocated for storing compressed pages' poitner should be
released after f2fs_write_compressed_pages(), otherwise it will
cause memory leak issue.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Fixes: 4c8ff709 ("f2fs: support data compression")
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>