Fix SkSurface cache.

Test: perfetto traces show > 5ms improvement
Change-Id: I49eb520566d0204bef85bf6d4a911d7e0db7aac4
diff --git a/libs/renderengine/skia/SkiaGLRenderEngine.cpp b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
index 8c5f0e6..07be0b6 100644
--- a/libs/renderengine/skia/SkiaGLRenderEngine.cpp
+++ b/libs/renderengine/skia/SkiaGLRenderEngine.cpp
@@ -486,7 +486,7 @@
     }
 
     auto grContext = mInProtectedContext ? mProtectedGrContext : mGrContext;
-    auto cache = mInProtectedContext ? mProtectedSurfaceCache : mSurfaceCache;
+    auto& cache = mInProtectedContext ? mProtectedSurfaceCache : mSurfaceCache;
     AHardwareBuffer_Desc bufferDesc;
     AHardwareBuffer_describe(buffer->toAHardwareBuffer(), &bufferDesc);
     LOG_ALWAYS_FATAL_IF(!hasUsage(bufferDesc, AHARDWAREBUFFER_USAGE_GPU_SAMPLED_IMAGE),