f2fs: zone: fix to don't trigger OPU on pinfile for direct IO

Otherwise, it breaks pinfile's sematics.

Cc: Daeho Jeong <daeho43@gmail.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>