msm: mdss: release rotator fence on unset

When rotator unset is called before rotator commit, the rotator
fences will never be signaled through rotator completion.
For this case need to release the sync fences as the source
buffers will no longer be used for this session.

Change-Id: I6eb7c871c67de1d4a78b6d66ba7d6d7bbd16c23a
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>