net: atlantic: use simple assignment in _get_stats and _get_sw_stats

This patch replaces addition assignment operator with a simple assignment
in aq_vec_get_stats() and aq_vec_get_sw_stats(), because it is
sufficient in both cases and this change simplifies the introduction of
u64_stats_update_* in these functions.

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>