Audio: fix compiler warning.

Eh, I'm not even able to do a single change without screwing up.

src/Magnum/Audio/Audio.cpp

@@ -35,7 +35,7 @@ namespace Magnum { namespace Audio {
 static_assert(std::is_same<ALubyte, UnsignedByte>::value, "ALubyte is not the same as UnsignedByte");
 /* ALbyte is defined as `signed char` in OpenAL Soft and `char` in the official
    SDK from Creative and on Apple. Both are okay. */
-static_assert(std::is_same<ALbyte, Byte>::value || std::is_signed<ALbyte>::value && sizeof(ALbyte) == 1, "ALbyte does not have the characteristics as Byte");
+static_assert(std::is_same<ALbyte, Byte>::value || (std::is_signed<ALbyte>::value && sizeof(ALbyte) == 1), "ALbyte does not have the characteristics as Byte");
 static_assert(std::is_same<ALushort, UnsignedShort>::value, "ALushort is not the same as UnsignedShort");
 static_assert(std::is_same<ALshort, Short>::value, "ALshort is not the same as Short");
 static_assert(std::is_same<ALuint, UnsignedInt>::value, "ALuint is not the same as UnsignedInt");