surfaceflinger: Fix -Wunused-variable compiler warning

Test: presubmit
Change-Id: I72a7d888cbaee4dd782ec43c1fc130669d9eb2ac

services/surfaceflinger/Scheduler/Scheduler.cpp

diff --git a/services/surfaceflinger/Scheduler/Scheduler.cpp b/services/surfaceflinger/Scheduler/Scheduler.cpp
index 68927bd..54ff2cd 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.cpp
+++ b/services/surfaceflinger/Scheduler/Scheduler.cpp
@@ -577,7 +577,8 @@
     if (!scheduleOpt) return;
     const auto& schedule = scheduleOpt->get();
 
-    if (const bool needMoreSignals = schedule->getController().addPresentFence(std::move(fence))) {
+    const bool needMoreSignals = schedule->getController().addPresentFence(std::move(fence));
+    if (needMoreSignals) {
         schedule->enableHardwareVsync();
     } else {
         constexpr bool kDisallow = false;