net: atlantic: rename AQ_NIC_RATE_2GS to AQ_NIC_RATE_2G5

This patch changes the constant name to a more logical "2G5"
(for 2.5G speeds).

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