Further template BlockDecimator by element type, use for audio buffer.

Appropriating for use as a buffer accumulator that will save up enough audio samples to put into an audio DMA buffer.

firmware/baseband/spectrum_collector.hpp

@@ -50,7 +50,7 @@ public:
 	);
 
 private:
-	BlockDecimator<256> channel_spectrum_decimator;
+	BlockDecimator<complex16_t, 256> channel_spectrum_decimator;
 	ChannelSpectrumFIFO fifo;
 
 	volatile bool channel_spectrum_request_update { false };