i40iw: Return correct max_fast_reg_page_list_len

Return correct value for max_fast_reg_page_list_len from
i40iw_query_device().

Signed-off-by: Faisal Latif <faisal.latif@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>