mtd: hyperbus: Make hyperbus_unregister_device() return void

mtd: hyperbus: Make hyperbus_unregister_device() return void

[ Upstream commit 0c90466a7985d39355f743e9cd2139da3e86c4d8 ]

The only thing that could theoretically fail in that function is
mtd_device_unregister(). However it's not supposed to fail and when
used correctly it doesn't. So wail loudly if it does anyhow.

This matches how other drivers (e.g. nand/raw/nandsim.c) use
mtd_device_unregister().

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

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/20220603210758.148493-2-u.kleine-koenig@pengutronix.de
Stable-dep-of: bf5821909eb9 ("mtd: hyperbus: hbmc-am654: fix an OF node reference leak")
Signed-off-by: Sasha Levin <sashal@kernel.org>