bcache: unregister reboot notifier if bcache fails to unregister device

bcache: unregister reboot notifier if bcache fails to unregister device

Orabug: stable_rc4

[ Upstream commit 2ecf0cdb2b437402110ab57546e02abfa68a716b ]

In bcache_init() function it forgot to unregister reboot notifier if
bcache fails to unregister a block device.  This commit fixes this.

Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Tested-by: Joshua Schmid <jschmid@suse.com>
Tested-by: Eric Wheeler <bcache@linux.ewheeler.net>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 322d0128f1e4af6b5b3532e0848fae633fd5a992)

Signed-off-by: Dan Duval <dan.duval@oracle.com>