iocost_monitor: print vrate inuse along with base_vrate

iocost_monitor: print vrate inuse along with base_vrate

The real vrate iocost inuse is not base_vrate, but the atomic vtime_rate.
We need iocost_monitor tool to display this real vrate that iocost use,
to check if the boosted compensated vrate is normal.

Effect after change:

nvme0n1 RUN  per=50.0ms cur_per=172116.580:v1040587.433 busy= +0 \
vrate=135.00%:270.00% params=ssd_dfl(CQ)
                ^
                |
         this is real vrate inuse

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lore.kernel.org/r/20230804065039.8885-2-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>