net: aquantia: make all files GPL-2.0-only

It was noticed some files had -or-later, however overall driver has
-only license. Clean this up.

Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>