mark pstore-blk as broken

mark pstore-blk as broken

pstore-blk just pokes directly into the pagecache for the block
device without going through the file operations for that by faking
up it's own file operations that do not match the block device ones.

As this breaks the control of the block layer of it's page cache,
and even now just works by accident only the best thing is to just
disable this driver.

Fixes: f9edd43ea779 ("pstore/blk: Introduce backend for block devices")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210608161327.1537919-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>