examples/io_uring-cp: wait for pending writes before exit copy loop
examples/io_uring-cp: wait for pending writes before exit copy loop

We could be ending the loop with all reads done, but with pending writes
that we haven't waited for yet. Ensure that we do so.

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing