i40iw: Use actual page size

In i40iw_post_send, use the actual page size instead of
encoded page size. This is to be consistent with the
rest of the file.

Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Henry Orosco <henry.orosco@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>