net: dsa: sja1105: fix configuration of source address learning

Due to a mistake, the driver always sets the address learning flag to
the previously stored value, and not to the currently configured one.
The bug is visible only in standalone ports mode, because when the port
is bridged, the issue is masked by .port_stp_state_set which overwrites
the address learning state to the proper value.

Fixes: 4d942354

 ("net: dsa: sja1105: offload bridge port flags to device")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>