io_uring: split slow path from io_queue_sqe

We don't want the slow path of io_queue_sqe to be inlined, so extract a
function from it.

   text    data     bss     dec     hex filename
  91950   13986       8  105944   19dd8 ./fs/io_uring.o
  91758   13986       8  105752   19d18 ./fs/io_uring.o

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/fb01253911f8fb374268f65b1ba939b54ca6583f.1632516769.git.asml.silence@gmail.com


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