Since commit 3efe41be ("mtd: implement common reboot notifier
boilerplate"), we might try to register a reboot notifier for an MTD
that failed to register. Let's avoid this by making the error path
clearer.
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>
Reviewed-by: NRichard Weinberger <richard@nod.at>