i40e: don't degrade __le16

Sparse cries when we compare an __le16 to a u16, almost like it cares
about architectures other than x86. Weird. Use the le16_to_cpu macro to
make it stop crying.

Change-ID: Id068f4d7868a2d3df234a791a76d15938f37db35
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>