Switch on the bio operation in zram_submit_bio and only call into
__zram_make_request for read and write operations.

Link: https://lkml.kernel.org/r/20230411171459.567614-6-hch@lst.deSigned-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>