soc: qcom: spcom: fix active pid clean up

A variable that is used to track active pid of the client using
the shared channel is cleaned up after releasing the mutex which
causes a race condition.
Changes are made to clean up the shared resource whlie the mutex
is still acquired.

Change-Id: If4b4277595dbcf39de628ad603134d16ae406cd6
Signed-off-by: Amandeep Virk <avirk@codeaurora.org>