f2fs: assign segments correctly for direct_io

commit bdb7d964c4fb73078ab21c20e8c7b7bf7e641bb6 upstream.

Previously, we assigned CURSEG_WARM_DATA for direct_io, but if we have two or
four logs, we do not use that type at all.
Let's fix it.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>