SF: Clean up DisplayDevice::initiateModeChange

Trace the pending mode after successfully setting it on HWC.

Remove unused status_t return value, and redundant warning log. Disallow
nullptr for out parameter.

Bug: 255635711
Test: presubmit
Change-Id: I381e5528d6336c300a80abcebccdd76369126c04
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 04088ec..11d48f6 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1397,11 +1397,7 @@
         constraints.seamlessRequired = false;
         hal::VsyncPeriodChangeTimeline outTimeline;
 
-        const auto status = display->initiateModeChange(*desiredModeOpt, constraints, &outTimeline);
-        if (status != NO_ERROR) {
-            // initiateModeChange may fail if a hotplug event is just about
-            // to be sent. We just log the error in this case.
-            ALOGW("initiateModeChange failed: %d", status);
+        if (!display->initiateModeChange(*desiredModeOpt, constraints, outTimeline)) {
             continue;
         }