The udata member of the kevent struct is a void *

Fixes the following warnings under clang:

loop_poll_kqueue.c:58:2: warning: incompatible integer to pointer conversion assigning to 'void *' from 'intptr_t' (aka 'long') [-Wint-conversion]

EV_SET(&ke, fd, filters, EV_ADD | EV_ENABLE, 0, 0, (intptr_t)pe);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/usr/include/sys/event.h:54:16: note: expanded from macro 'EV_SET'

(kevp)->udata = (f);                    \
              ^ ~~~