AT_CellularDevice.cpp - unused variable err warning

We get this compiler warning;

Compile [  7.9%]: AT_CellularDevice.cpp
[Warning] AT_CellularDevice.cpp@206,18: variable 'err' set but not used [-Wunused-but-set-variable]

Due to the fact, that the code that would actually use this variable
is behind trace flags. Moving the definition to be behind that same
flag resolves the issue.

Author: Janne Kiiskila

features/cellular/framework/AT/AT_CellularDevice.cpp

@@ -203,7 +203,6 @@ nsapi_error_t AT_CellularDevice::get_sim_state(SimState &state)
     _at->flush();
     nsapi_error_t error = _at->at_cmd_str("+CPIN", "?", simstr, sizeof(simstr));
     ssize_t len = strlen(simstr);
-    device_err_t err = _at->get_last_device_error();
     _at->unlock();
 
     if (len != -1) {
@@ -230,6 +229,7 @@ nsapi_error_t AT_CellularDevice::get_sim_state(SimState &state)
             tr_error("SIM PUK required");
             break;
         case SimStateUnknown:
+            device_err_t err = _at->get_last_device_error();
             if (err.errType == DeviceErrorTypeErrorCME && err.errCode == 14) {
                 tr_info("SIM busy");
             } else {