iavf: remove an unneeded variable

The variable `ret_code' used for returning is never changed in function
`iavf_shutdown_adminq'. So that it can be removed and just return its
initial value 0 at the end of `iavf_shutdown_adminq' function.
Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/iavf/iavf_adminq.c

@@ -551,15 +551,13 @@ enum iavf_status iavf_init_adminq(struct iavf_hw *hw)
  **/
 enum iavf_status iavf_shutdown_adminq(struct iavf_hw *hw)
 {
-	enum iavf_status ret_code = 0;
-
 	if (iavf_check_asq_alive(hw))
 		iavf_aq_queue_shutdown(hw, true);
 
 	iavf_shutdown_asq(hw);
 	iavf_shutdown_arq(hw);
 
-	return ret_code;
+	return 0;
 }
 
 /**