f2fs: fix to calculate dirty data during has_not_enough_free_secs()

In lfs mode, dirty data needs OPU, we'd better calculate lower_p and
upper_p w/ them during has_not_enough_free_secs(), otherwise we may
encounter out-of-space issue due to we missed to reclaim enough
free section w/ foreground gc.

Fixes: 36abef4e ("f2fs: introduce mode=lfs mount option")
Cc: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>