We currently use it for find_or_create_page(), which means that it
cannot fail. Ensure we also pass in 'retry == true' to
alloc_page_buffers(), which also ensure that it cannot fail.

After this, there are no failure cases in grow_dev_page() that
occur because of a failed memory allocation.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>