staging: fsl-dpaa2/eth: Remove unused fields from priv struct

Remove the dpni_id and buffer_layout fields from device's
private structure. They're only used at probe so we don't
need to store them for further use.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>