drivers: soc: qcom: fix underflow in read_event

in function read_event, total can be less than previous count as
cached_total_count is not always updated.
Fix this by updating cached_total_count in read_event
when CPU is not idle.

Change-Id: I76a92a41cc6d79eb55c02f96025950576a5c5808
Signed-off-by: Shivnandan Kumar <kshivnan@codeaurora.org>