We can't assume that the whole batch has fixed files in it. If it's a
mix, or none at all, then we can end up doing a ref put that either
messes up accounting, or causes an oops if we have no fixed files at
all.

Also ensure we free requests properly between inflight accounted and
normal requests.

Fixes: 82c721577011 ("io_uring: extend batch freeing to cover more cases")
Reported-by: NDmitrii Dolgov <9erthalion6@gmail.com>
Reported-by: NPavel Begunkov <asml.silence@gmail.com>
Tested-by: NDmitrii Dolgov <9erthalion6@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>