net: aquantia: fixed memcpy size

Not careful array dereference caused analysis tools
to think there could be memory overflow.

There was actually no corruption because the array is
two dimensional.

drivers/net/ethernet/aquantia/atlantic/aq_ethtool.c: 140
  aq_ethtool_get_strings() error:
    memcpy() '*aq_ethtool_stat_names' too small (32 vs 704)

Signed-off-by: Nikita Danilov <nikita.danilov@aquantia.com>
Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>