net: dsa: make the STP state function return void

The DSA layer doesn't care about the return code of the port_stp_update
routine, so make it void in the layer and the DSA drivers.

Replace the useless dsa_slave_stp_update function with a
dsa_slave_stp_state function used to reply to the switchdev
SWITCHDEV_ATTR_ID_PORT_STP_STATE attribute.

In the meantime, rename port_stp_update to port_stp_state_set to
explicit the state change.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6352.c b/drivers/net/dsa/mv88e6352.c
index 5f528ab..7f452e4 100644
--- a/drivers/net/dsa/mv88e6352.c
+++ b/drivers/net/dsa/mv88e6352.c
@@ -326,7 +326,7 @@
 	.get_regs		= mv88e6xxx_get_regs,
 	.port_bridge_join	= mv88e6xxx_port_bridge_join,
 	.port_bridge_leave	= mv88e6xxx_port_bridge_leave,
-	.port_stp_update	= mv88e6xxx_port_stp_update,
+	.port_stp_state_set	= mv88e6xxx_port_stp_state_set,
 	.port_vlan_filtering	= mv88e6xxx_port_vlan_filtering,
 	.port_vlan_prepare	= mv88e6xxx_port_vlan_prepare,
 	.port_vlan_add		= mv88e6xxx_port_vlan_add,