staging: fsl-dpaa2/eth: fix a couple of implicit includes

dpni.c is using byte order macros and error codes but does
not explicitly include the required kernel header, so add it.

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