Revert "mark pstore-blk as broken"

This reverts commit d07f3b08.

pstore-blk was fixed to avoid the unwanted APIs in commit 7bb9557b


("pstore/blk: Use the normal block device I/O path"), which landed in
the same release as the commit adding BROKEN.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20211116181559.3975566-1-keescook@chromium.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>