cfq-iosched: Charge at least 1 jiffie instead of 1 ns

cfq-iosched: Charge at least 1 jiffie instead of 1 ns

Commit bc5240ca5bc1 (cfq-iosched: Convert from jiffies to nanoseconds)
could result in charging just 1 ns to a cgroup submitting IO instead of 1
jiffie we always charged before. It is arguable what is the right amount
to change but for now lets retain the old behavior of always charging at
least one jiffie.

Fixes: bc5240ca5bc1c224de225212da9f8378fd604e99
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>