bcache: cached_dev_free needs to put the sb page

bcache: cached_dev_free needs to put the sb page

BugLink: https://bugs.launchpad.net/bugs/1864488
[ Upstream commit e8547d42095e58bee658f00fef8e33d2a185c927 ]

Same as cache device, the buffer page needs to be put while
freeing cached_dev.  Otherwise a page would be leaked every
time a cached_dev is stopped.

Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>