net: atlantic: use __packed instead of the full expansion.

This patches fixes the review comment made by Jakub Kicinski
in the "net: atlantic: A2 support" patch series.

Signed-off-by: Mark Starovoytov <mstarovoitov@marvell.com>
Signed-off-by: Igor Russkikh <irusskikh@marvell.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>