Enable -Wconversion in BufferStateLayer.

Bug: 129481165
Test: make, atest libsurfaceflinger_unittest
Change-Id: I589add0afb21332a0bc2a4b20f5e8ee8fc85208c
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 0ac6438..e335e56 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -942,7 +942,7 @@
         return width > mMaxRenderTargetSize || height > mMaxRenderTargetSize;
     }
 
-    int getMaxAcquiredBufferCountForCurrentRefreshRate(uid_t uid) const;
+    uint32_t getMaxAcquiredBufferCountForCurrentRefreshRate(uid_t uid) const;
 
     /*
      * Display and layer stack management