dpaa2-eth: name the debugfs directory after the DPNI object

Name the debugfs directory after the DPNI object instead of the netdev
name since this can be changed after probe by udev rules.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>