sdm: Set vsync_registered_ to false in SetEventState

Set vsync_registered_ to false in SetEventState. In the chance
that HandleVsync does not get called by driver, we may fall in
state where vsync_registered_ never updates to false.

CRs-Fixed: 2615875
Change-Id: I033e46d9b79e0ffc320ff89c7847fb6d9ba12421
diff --git a/sdm/libs/core/drm/hw_events_drm.cpp b/sdm/libs/core/drm/hw_events_drm.cpp
index 4bbf001..627d6f4 100644
--- a/sdm/libs/core/drm/hw_events_drm.cpp
+++ b/sdm/libs/core/drm/hw_events_drm.cpp
@@ -290,6 +290,8 @@
           return error;
         }
         vsync_registered_ = true;
+      } else if (!vsync_enabled_) {
+        vsync_registered_ = false;
       }
     } break;
     default: