[roll] Roll fuchsia [display] Avoid UAF from vsync thread

The hardware display driver can call into the core display driver (and
cause a UAF) if it receives a vsync event after the core display driver
is released. To prevent that, the hardware driver needs to implement
DdkChildPreRelease and clear out it child protocol pointer at that
point.

Original-Fixed: 65603
Multiply: fake_hdcp_tests
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/467138
Original-Revision: ec6a636b4befe6d39354fec14a4731c72be4aa9d
GitOrigin-RevId: dab1edcf189a924475908866cd27a97a85d1f16c
Change-Id: Ifef9d412d11624ef1191296f5e7e0d3dbce7b1d5
diff --git a/stem b/stem
index 4b16c1e..3696fc0 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="3f3063dd684ef5dc44be55ed5140c1743ae12477"/>
+             revision="ec6a636b4befe6d39354fec14a4731c72be4aa9d"/>
   </projects>
   <hooks>
     <hook name="install-fx"