eta: make CR= display more easy to understand

eta: make CR= display more easy to understand

Currently we sum up read and write IOPS/BW rates, but that reads
a bit strange when a given workload only does reads OR writes.
The user then thinks that fio mis-parsed the setting, reading
twice as much as expected.

Only sum up for the read OR write side if one direction is given.
For a mixed workload, it's still the sum of both.

Signed-off-by: Jens Axboe <axboe@kernel.dk>