rtc: cros-ec: Only warn once in .remove() about notifier_chain problems

When a remove platform device callback returns an error code, the driver
core emits an error message ("remove callback returned a non-zero value.
This will be ignored.\n") and still removes the device. As the driver
already emits a more specific error message, return 0 to suppress the
core's error message.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220707153156.214841-1-u.kleine-koenig@pengutronix.de