i40e: remove the useless value assignment in i40e_clean_adminq_subtask

The variable ret is overwritten by the following call
i40e_clean_arq_element() and the assignment is useless, so remove it.

Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>