msm: sde: Fix SMMU fault in SDE rotator for secure playback

When playing secure content, framebuffer is setup as secure in the
rotator. But the sw timestamp is not going through the secure
route, and must clear out the secure setting, otherwise a smmu fault
will be issued. This fix make sure the secure buffer status is
cleared during the sw timestamp submission.

CRs-Fixed: 1059620
Change-Id: Ifb0f9928fa1d948351e6fc1ad925a070a7f50a96
Signed-off-by: Benjamin Chan <bkchan@codeaurora.org>