soc: qcom: glink_ssr: Initialize waitqueue in probe function

waitqueue is initialized on every call to notify_for_subsystem.
This leads to stability issue if one thread is waiting for completion
and another thread re-initializes it.

Waitqueue is initialized only in probe function.

CRs-Fixed: 2197181
Change-Id: I3509a7c4a197c727b2025c1aeb6a35690c3c8501
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>