net: atlantic: Replace ENOTSUPP usage to EOPNOTSUPP

This patch replaces ENOTSUPP (where it was used by mistake) with
EOPNOTSUPP.

Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>