SF: Avoid a few nullable sp<DisplayDevice> params

Bug: 255635821
Test: Build
Change-Id: I6c84b89d8b532eca581530931a8b876c37ca3189
diff --git a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
index e03f6cc..282c87e 100644
--- a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
+++ b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
@@ -473,7 +473,7 @@
         return mFlinger->setDesiredDisplayModeSpecs(displayToken, specs);
     }
 
-    void onActiveDisplayChanged(const sp<DisplayDevice>& activeDisplay) {
+    void onActiveDisplayChanged(const DisplayDevice& activeDisplay) {
         Mutex::Autolock lock(mFlinger->mStateLock);
         ftl::FakeGuard guard(kMainThreadContext);
         mFlinger->onActiveDisplayChangedLocked(nullptr, activeDisplay);