iavf: use appropriate enum for comparison

adapter->link_speed has type enum virtchnl_link_speed but our comparisons
are against enum iavf_aq_link_speed. Though they are, currently, the same
values, change the comparison to the matching enum virtchnl_link_speed
since that may not always be the case.

Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Piotr Kwapulinski <piotr.kwapulinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>