Add missing parameter to aften_encode_frame() call

Problem:
int res = aften_encode_frame(&fAftenContext, fAC3Buffer + SPDIF_HEADER_SIZE, fSampleBuffer);
Fails, because API is
AFTEN_API int aften_encode_frame(AftenContext *s, unsigned char *frame_buffer,const void *samples, int count)

The additional parameter 'count' was added to libaften function aften_encode_frame() here:
e1cbb66628 (diff-d4868af7d235a914aef2ec4f979fcb9fR87)

Solves https://github.com/jackaudio/jack2/issues/455

common/JackAC3Encoder.cpp

@@ -126,7 +126,7 @@ void JackAC3Encoder::Process(float** inputs_buffer, float** outputs_buffer, int
 			}  
 			
 			// use interleaved version
-            int res = aften_encode_frame(&fAftenContext, fAC3Buffer + SPDIF_HEADER_SIZE, fSampleBuffer);
+            int res = aften_encode_frame(&fAftenContext, fAC3Buffer + SPDIF_HEADER_SIZE, fSampleBuffer, nframes);
             if (res < 0) {
                 jack_error("aften_encode_frame error !!");
                 return;