Fix USRP1 build with support for setting Rx/TxAntenna

The USRP1 build was broken by commit 77ce99ac67.

Commit 77ce99ac67 broke the USRP1 build

Change-Id: I28585947d5662cdd580a814cce54a5d9aa30eeb8
(cherry picked from commit 3f52f0e6c5)

Transceiver52M/USRPDevice.h

@@ -198,6 +198,7 @@ private:
   inline double numberRead() { return samplesRead; }
   inline double numberWritten() { return samplesWritten; }
 
+  std::vector<std::string> tx_paths, rx_paths;
 };
 
 #endif // _USRP_DEVICE_H_