net: dsa: qca8k: enable EEE once

If EEE is queried enabled, qca8k_set_eee calls qca8k_eee_enable_set
twice (because it is already called in qca8k_eee_init). Fix that.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>