zram: return errors from read_from_bdev_sync

Propagate read errors to the caller instead of dropping them on the floor,
and stop returning the somewhat dangerous 1 on success from
read_from_bdev*.

Link: https://lkml.kernel.org/r/20230411171459.567614-18-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>