tcpm: allow looking for role_sw device in the main node

If ports are defined in the tcpc main node, fwnode_usb_role_switch_get()
returns an error, meaning usb_role_switch_get() (which would succeed)
never gets a chance to run as port->role_sw isn't NULL, causing a
regression on devices where this is the case.

Fix this by turning the NULL check into IS_ERR_OR_NULL(), so
usb_role_switch_get() can actually run and the device get properly probed.

Fixes: 2d8713f807a4 ("tcpm: switch check for role_sw device with fw_node")
Cc: stable <[e-mail]>
Reviewed-by: Heikki Krogerus <[e-mail]>
Reviewed-by: Dragan Simic <[e-mail]>
Signed-off-by: Arnaud Ferraris <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/typec/tcpm/tcpm.c

···
 	port->partner_desc.identity = &port->partner_ident;
 
 	port->role_sw = fwnode_usb_role_switch_get(tcpc->fwnode);
-	if (!port->role_sw)
+	if (IS_ERR_OR_NULL(port->role_sw))
 		port->role_sw = usb_role_switch_get(port->dev);
 	if (IS_ERR(port->role_sw)) {
 		err = PTR_ERR(port->role_sw);