mtd: rawnand: omap2: Suppress error message after WARN in .remove()

Returning an error value in a platform remove callback results in an error
message being emitted by the platform core, but otherwise it doesn't make
a difference. After the WARN splat this generic error message doesn't add
any value, so return 0 unconditionally

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220603210758.148493-10-u.kleine-koenig@pengutronix.de