io_uring: account drain memory to cgroup

Account drain allocations against memcg. It's not a big problem as each
such allocation is paired with a request, which is accounted, but it's
nicer to follow the limits more closely.

Cc: stable@vger.kernel.org # 6.1
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f8dfdbd755c41fd9c75d12b858af07dfba5bbb68.1746788718.git.asml.silence@gmail.com


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