Transceiver52M: Allow setting gain before POWERON

There is no reason gain settings should not be modifiable when the radio
is running or not.

Signed-off-by: Tom Tsou <tom@tsou.cc>
diff --git a/Transceiver52M/radioInterface.h b/Transceiver52M/radioInterface.h
index b88fe6b..877102f 100644
--- a/Transceiver52M/radioInterface.h
+++ b/Transceiver52M/radioInterface.h
@@ -120,7 +120,7 @@
   /** drive reception of GSM bursts */
   bool driveReceiveRadio();
 
-  void setPowerAttenuation(double atten, size_t chan = 0);
+  int setPowerAttenuation(int atten, size_t chan = 0);
 
   /** returns the full-scale transmit amplitude **/
   double fullScaleInputValue();