Maybe make a smaller diff by checking for timo == -1 in here? That is, just

while (...) {
    if (timo == -1) {
        error = EWOULDBLOCK;
        break;
    }
}

I've seen this pattern in other places in the kernel. Often the sleep is done in the else in this case. Also, even though EGAIN == EWOULDBLOCK on FreeBSD, EWOULDBLOCK (or EINPROGRESS) better matches the existing error descriptions in the aio_waitcomplete(2) manpage. It is also what other places in the kernel use when skipping a sleep due to a poll.