blk-iocost: fix incorrect vtime comparison in iocg_is_idle()

commit dcd6589b11d3b1e71f516a87a7b9646ed356b4c0 upstream.

vtimes may wrap and time_before/after64() should be used to determine
whether a given vtime is before or after another. iocg_is_idle() was
incorrectly using plain "<" comparison do determine whether done_vtime
is before vtime. Here, the only thing we're interested in is whether
done_vtime matches vtime which indicates that there's nothing in
flight. Let's test for inequality instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 7caa4715 ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>