We can't touch a bio after ->make_request_fn(), for all we know it could
already have been completed by the time this function returns.

This reverts commit 698cef17.

Reported-by:  <syzbot+4df6ca820108fd248943@syzkaller.appspotmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>