greybus: Revert "gb_loopback: Fix throughput calculations"

This reverts commit 9b9b046af237f5674c2f7ca991dc62332b2d4041

Bryan wants more feedback first.

Reported-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>