f2fs: fix to clear unusable_cap for checkpoint=enable

mount -t f2fs -o checkpoint=disable:10% /dev/vdb /mnt/f2fs/
mount -t f2fs -o remount,checkpoint=enable /dev/vdb /mnt/f2fs/

kernel log:
F2FS-fs (vdb): Adjust unusable cap for checkpoint=disable = 204440 / 10%

If we has assigned checkpoint=enable mount option, unusable_cap{,_perc}
parameters of checkpoint=disable should be reset, then calculation and
log print could be avoid in adjust_unusable_cap_perc().

Fixes: 1ae18f71 ("f2fs: fix checkpoint=disable:%u%%")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>