Fix -Wclass-memaccess warnings

We want to clear/memset the padding bytes, not just each member,
so using assignment or {} initialization is not an option.

To silence the warnings, cast the object pointer to u8* (which is not
undefined behavior) to make it explicit to the compiler that we want
to fill the object representation.

Source/Core/VideoCommon/BPStructs.cpp

@@ -43,7 +43,7 @@ static const float s_gammaLUT[] = {1.0f, 1.7f, 2.2f, 1.0f};
 
 void BPInit()
 {
-  memset(&bpmem, 0, sizeof(bpmem));
+  memset(reinterpret_cast<u8*>(&bpmem), 0, sizeof(bpmem));
   bpmem.bpMask = 0xFFFFFF;
 }