msm: dcvs: do not run gpu set_floor_frequency callbacks after stop_sink

Once a gpu calls stop_sink and is no longer participating in dcvs, we
should not call set_floor_frequency callbacks for that gpu.

Change-Id: I3cde82dc9975bcb37f065ea7ab8eb88a8f7fc933
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>