zram: do not forget to endio for partial discard requests

As reported by Qu Wenruo and Avinesh Kumar, the following

getconf PAGESIZE
65536
blkdiscard -p 4k /dev/zram0

takes literally forever to complete. zram doesn't support partial
discards and just returns immediately w/o doing any discard work in such
cases. The problem is that we forget to endio on our way out, so
blkdiscard sleeps forever in submit_bio_wait(). Fix this by jumping to
end_bio label, which does bio_endio().

Link: https://lore.kernel.org/20260331074255.777019-1-senozhatsky@chromium.org
Fixes: 0120dd6e4e20 ("zram: make zram_bio_discard more self-contained")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Qu Wenruo <wqu@suse.com>
Closes: https://lore.kernel.org/linux-block/92361cd3-fb8b-482e-bc89-15ff1acb9a59@suse.com
Tested-by: Qu Wenruo <wqu@suse.com>
Reported-by: Avinesh Kumar <avinesh.kumar@suse.com>
Closes: https://bugzilla.suse.com/show_bug.cgi?id=1256530
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>