fixing soyosource data frame

There was an error in an old fix, that solved wrong values in small demands < 20 W. But introduced errors around 250 / 500 W.
This one is tested with 3 different hardware versions and no anomaly was found anymore.

zeroinput.py

@@ -65,7 +65,9 @@ def set_soyo_demand(ser,power):	# create the packet for soyosource gti
 	pu = power >> 8
 	pl = power & 0xFF
 	cs = 264 - pu - pl
-	if cs >= 256: cs = 8
+	if cs > 255: 
+		if power > 250:	cs -= 256
+		else:		cs -= 255
 
 	ser.write( bytearray([0x24,0x56,0x00,0x21,pu,pl,0x80,cs]) )
 	ser.flush()