i40evf: don't violate scope

Move a declaration up one level so we don't dereference it out of scope.
This didn't cause any panics, but the details->async field would
mysteriously disappear, causing unnecessary delays when sending AQ
commands. Also, the code is just plain wrong.

Change-ID: I753f64f13c55e5d75ea4351e29b14fb53b2f0104
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>