Common: Maintain C++11 support in sign extend.

Core/HLE/sceKernelModule.cpp

@@ -626,7 +626,7 @@ static void WriteVarSymbol(WriteVarSymbolState &state, u32 exportAddress, u32 re
 	case R_MIPS_LO16:
 		{
 			// Sign extend the existing low value (e.g. from addiu.)
-			const u32 offsetLo = SignExtend16To32(relocData);
+			const u32 offsetLo = SignExtend16ToU32(relocData);
 			u32 full = exportAddress;
 			// This is only used in the error case (no hi/wrong hi.)
 			if (!reverse) {