IB/i40iw: Remove a superfluous assignment statement

Due to a previous patch initializing ib_device.dev.parent is
sufficient and initializing dma_device is no longer needed.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Faisal Latif <faisal.latif@intel.com>
Cc: Shiraz Saleem <shiraz.saleem@intel.com>
Acked-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>