f2fs: let FI_OPU_WRITE override FADVISE_COLD_BIT

Cold files may be fragmented due to SSR, defragment is needed as
sequential reads are dominant scenarios of these files. FI_OPU_WRITE
should override FADVISE_COLD_BIT to avoid defragment fails.

Signed-off-by: Weichao Guo <guoweichao@oppo.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>