STAGING: octeon-ethernet: Fix compile error caused by skb_frag_struct change

Evidently the definition of struct skb_frag_struct has changed, so we
need to change to match it.

Signed-off-by: David Daney <david.daney@cavium.com>
To: netdev@vger.kernel.org
To: gregkh@suse.de
To: devel@driverdev.osuosl.org
Patchwork: https://patchwork.linux-mips.org/patch/2909/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>