io_uring: use right issue_flags for splice/tee

Pass right issue_flags into into io_file_get_fixed() instead of
IO_URING_F_UNLOCKED. It's probably not a problem at the moment but let's
do it safer.

Fixes: 6bf9c47a

 ("io_uring: defer file assignment")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7d242daa9df5d776907686977cd29fbceb4a2d8d.1649862516.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>