tcpm: allow looking for role_sw device in the main node

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 <stable@kernel.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>
Link: https://patch.msgid.link/20260105-fix-ppp-power-v2-1-6924f5a41224@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>