staging: octeon-ethernet: eliminate OCTEON_ETHERNET_VERSION

This driver has drifted away from out-of-tree versions years ago
and the version string does not provide any useful information.
Instead provide the kernel version string to ethtool, so that we get
useful version information e.g. for bug reports.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>