i40e: convert ret to aq_ret

When calling admin queue functions the driver should use aq_ret
variable to help make clear that the return value is not a regular
return variable.

This allows for clean up of the return types that were previously
converted to int.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>