tvhpoll: Fix building on FreeBSD i386

src/tvhpoll.c: In function 'tvhpoll_add':
src/tvhpoll.c:124: warning: cast to pointer from integer of different size
src/tvhpoll.c:127: warning: cast to pointer from integer of different size
src/tvhpoll.c: In function 'tvhpoll_wait':
src/tvhpoll.c:180: warning: cast from pointer to integer of different size