serdev: Fix serdev_uevent failure on ACPI enumerated serdev-controllers

ACPI enumerated serdev-controllers do not have an ACPI companion, the ACPI
companion belongs to the serdev-device child of the serdev-controller, not
to the controller itself. This was causing serdev_uevent to always return
-ENODEV when called on a serdev-controller leading to errors like these:

kernel: serial serial0: uevent: failed to send synthetic uevent

being logged. This commit modifies serdev_uevent to directly return 0
when called on an ACPI enumerated serdev-controller fixing this.

Note: I do not think that setting a modalias on a devicetree enumerated
serdev-controller makes sense either. So perhaps the !dev->of_node part of
the check can be dropped too, but I'm not entirely sure that doing this
on devicetree too is correct.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serdev/core.c

@@ -54,6 +54,11 @@ static int serdev_uevent(struct device *dev, struct kobj_uevent_env *env)
 	int rc;
 
 	/* TODO: platform modalias */
+
+	/* ACPI enumerated controllers do not have a modalias */
+	if (!dev->of_node && dev->type == &serdev_ctrl_type)
+		return 0;
+
 	rc = acpi_device_uevent_modalias(dev, env);
 	if (rc != -ENODEV)
 		return rc;