perf tools: Properly set the value of 'old' in snapshot mode

In snapshot mode the value of the 'old' pointer needs to be adjusted when
'head' has wrapped around in order to get the latest information in the
buffer and be compatible with the generic AUX ring buffer mechanic.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
1 file changed