io_uring: optimise hot path restricted checks

Move likely/unlikely from io_check_restriction() to specifically
ctx->restricted check, because doesn't do what it supposed to and make
the common path take an extra jump.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/22bf70d0a543dfc935d7276bdc73081784e30698.1624739600.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>