ax88796c: fix ioctl callback

The timestamp ioctls are now handled by the ndo_eth_ioctl() callback,
not the old ndo_do_ioctl(), but oax88796 introduced the
function for the old way.

Move it over to ndo_eth_ioctl() to actually allow calling it from
user space.

Fixes: a97c69ba ("net: ax88796c: ASIX AX88796C SPI Ethernet Adapter Driver")
Fixes: a7605370 ("dev_ioctl: split out ndo_eth_ioctl")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Lukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>