[opengl] Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: Ia2f91707b277954d5105f6fdb489caad9ef8848c
diff --git a/opengl/tests/lib/WindowSurface.cpp b/opengl/tests/lib/WindowSurface.cpp
index 2b76279..b06422a 100644
--- a/opengl/tests/lib/WindowSurface.cpp
+++ b/opengl/tests/lib/WindowSurface.cpp
@@ -57,7 +57,7 @@
     sp<SurfaceControl> sc = surfaceComposerClient->createSurface(
             String8("Benchmark"), width, height,
             PIXEL_FORMAT_RGBX_8888, ISurfaceComposerClient::eOpaque);
-    if (sc == NULL || !sc->isValid()) {
+    if (sc == nullptr || !sc->isValid()) {
         fprintf(stderr, "Failed to create SurfaceControl\n");
         return;
     }