Disable -Wunused-value for surfaceflinger

```
frameworks/native/services/surfaceflinger/Display/DisplayModeController.cpp:293:14: error: ignoring temporary created by a constructor declared with 'nodiscard' attribute [-Werror,-Wunused-value]
  293 |             (std::scoped_lock(displayPtr->desiredModeLock), displayPtr->desiredModeOpt)
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Change-Id: I5e84dbd628f5c03f5e325f5ccc5d365d2f40c9dd
Flag: EXEMPT b/369277774
Bug: b/369277774
(cherry picked from commit 4648b7e)

Author: appujee

services/surfaceflinger/Display/DisplayModeController.cpp

@@ -283,6 +283,8 @@ void DisplayModeController::updateKernelIdleTimer(PhysicalDisplayId displayId,
     }
 }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-value" // b/369277774
 auto DisplayModeController::getKernelIdleTimerState(PhysicalDisplayId displayId) const
         -> KernelIdleTimerState {
     std::lock_guard lock(mDisplayLock);
@@ -298,4 +300,5 @@ auto DisplayModeController::getKernelIdleTimerState(PhysicalDisplayId displayId)
     return {desiredModeIdOpt, displayPtr->isKernelIdleTimerEnabled};
 }
 
+#pragma clang diagnostic pop
 } // namespace android::display