alsa: log period and buffer size

Log the real period and buffer size.  This might be useful when
debugging xruns.  Note that the same information is available in
/proc/asound/card*/pcm*p/sub*/hw_params

src/output/alsa_plugin.c

@@ -369,6 +369,9 @@ configure_hw:
 	if (err < 0)
 		goto error;
 
+	g_debug("buffer_size=%u period_size=%u",
+		(unsigned)alsa_buffer_size, (unsigned)alsa_period_size);
+
 	return true;
 
 error: