net: ethernet: ave: Replace alloc_etherdev() with devm_alloc_etherdev()

Use devm_alloc_etherdev() to simplify the code instead of alloc_etherdev().

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>