staging: fsl-dpaa2/eth: Remove unused field

Remove dpio_id field in struct dpaa2_eth_channel, which wasn't
used anywhere in the code.

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