io_uring: rename io_sqe_file_register

Rename io_sqe_file_register(), so the name better reflects what the
function is doing.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d5091518883786969e244d2f0854a47bbdaa5061.1649334991.git.asml.silence@gmail.com


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