io_uring: kill io_put_req_deferred()

We have several spots where a call to io_fill_cqe_req() is immediately
followed by io_put_req_deferred(). Replace them with
__io_req_complete_post() and get rid of io_put_req_deferred() and
io_fill_cqe_req().

> size ./fs/io_uring.o
   text    data     bss     dec     hex filename
  86942   13734       8  100684   1894c ./fs/io_uring.o
> size ./fs/io_uring.o
   text    data     bss     dec     hex filename
  86438   13654       8  100100   18704 ./fs/io_uring.o

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/10672a538774ac8986bee6468d960527af59169d.1650056133.git.asml.silence@gmail.com


[axboe: fold in followup fix]
Signed-off-by: Jens Axboe <axboe@kernel.dk>