i40e: get rid of magic number

We have a define for this, use it. No functional change.

Change-ID: Ic0e3ea4f562e46de63b2a8de07f291ccc10205fd
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>