tools/tracing/rtla: osnoise_hist: use total duration for average calculation

tools/tracing/rtla: osnoise_hist: use total duration for average calculation

[ Upstream commit 3c5e0981d20ffb42d1ad4505a69ade8f492004cd ]

Sampled durations must be weighted by observed quantity, to arrive at a correct
average duration value.

Perform calculation of total duration by summing (duration * count).

Link: https://lkml.kernel.org/r/20230103103400.275566-2-br015@umbiko.net
Fixes: 68cee15f86dc ("rtla/osnoise: Add the hist mode")
Signed-off-by: Andreas Ziegler <br015@umbiko.net>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>