output/openal: convert macro to constexpr

src/output/plugins/OpenALOutputPlugin.cxx

@@ -34,12 +34,12 @@
 #include <OpenAL/alc.h>
 #endif
 
-/* should be enough for buffer size = 2048 */
-#define NUM_BUFFERS 16
-
 class OpenALOutput {
 	friend struct AudioOutputWrapper<OpenALOutput>;
 
+	/* should be enough for buffer size = 2048 */
+	static constexpr unsigned NUM_BUFFERS = 16;
+
 	AudioOutput base;
 
 	const char *device_name;