uhd: add missing return in device open

Fixes a compile warning; returns true if all is goes well.

Signed-off-by: Thomas Tsou <ttsou@vt.edu>

public-trunk/Transceiver/UHDDevice.cpp

@@ -275,6 +275,8 @@ bool UHDDevice::open()
 
 	// Print configuration
 	LOG(INFO) << usrpDevice->get_pp_string();
+
+	return true;
 }