soc: qcom: spcom: Fix pid management for shared channel

In case of multi client support for channel access in
the spcom, ensure correct pid is saved upon client
registration and removed upon client deregistration.

Change-Id: I4ecd627aca87fdeb1e33b1cd08b988d0511e1908
Signed-off-by: Amandeep Virk <avirk@codeaurora.org>