i40iw: Correct and use size parameter to i40iw_reg_phys_mr

Fix size parameter passed to i40iw_reg_phys_mr and use it to
register memory.

Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>