i40e: trivial fixup of comments in i40e_xsk.c

The comment above i40e_run_xdp_zc() was clearly copy-pasted from
function i40e_xsk_umem_setup, which is just above.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>