Use derived variable size for memcpy

Manually cherry-picked from aom/master:
bf2ad75a1723d223c376b93295aa06dd23226937

Change-Id: I99f05e79ec8ad35a49bc124e6dd829ccc7d9cc36

test/convolve_test.cc

@@ -396,8 +396,8 @@ class ConvolveTest : public ::testing::TestWithParam<ConvolveParam> {
   void CopyOutputToRef() {
     memcpy(output_ref_, output_, kOutputBufferSize);
 #if CONFIG_AOM_HIGHBITDEPTH
-    memcpy(output16_ref_, output16_,
-           kOutputBufferSize * sizeof(output16_ref_[0]));
+    // Copy 16-bit pixels values. The effective number of bytes is double.
+    memcpy(output16_ref_, output16_, sizeof(output16_[0]) * kOutputBufferSize);
 #endif
   }