i40e/i40evf: check AQ register for valid data

B0 Si blocks AQ registers when in Blank Flash mode - write is dropped,
read gives 0xDEADBEEF. Introduce a simple check for a correct value in one
of the AQ registers to be sure that AQ was configured correctly.
Without this check we get into an endless loop while trying to send
GetVersion AQ cmd.

Change-ID: I00102b8c5fa6c16d14289be677aafadf87f10f0d
Signed-off-by: Kamil Krawczyk <kamil.krawczyk@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>