leds: lm3601x: Improve error reporting for problems during .remove()

Returning an error value in an i2c remove callback results in a generic
error message being emitted by the i2c core, but otherwise it doesn't
make a difference. The device goes away anyhow and the devm cleanups are
called.

So instead of triggering the generic i2c error message, emit a more
helpful message if a problem occurs and return 0 to suppress the generic
message.

This patch is a preparation for making i2c remove callbacks return void.

Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>