msm: dcvs: drop pending frequency update on stop sink

If there is a pending frequency update when a core stops
acting as a dcvs sink, it should just be dropped, rather
than trying to honor that last frequency request.

Change-Id: Iac30cc7e06a8a70eecc4da712fdf160b788a7c2c
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>