realtime_back.py: store output processed on a variable
realtime_back.py: store output processed on a variable

The variable will be used later for other purposes. This
change introduces no functional changes.

Signed-off-by: Luis Chamberlain <d4fa18192c5a479e564d29c2300c2e15afd1d8d7@kernel.org>

01org/fiovisualizer,01org/fiovisualizer