In function i40e_debug_aq parameter desc is assumed to be
possibly NULL. Do not dereference it before checking the
value.

Fixes: f905dd62 ("i40e/i40evf: add max buf len to aq debug print helper")
Signed-off-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>