Have dummy_forced_read only if it's used

[maskit]

dummy_forced_read is unused if SANITY is not defined, and compilers warn unused function. The function is used like this (surrounded by ifdef SANITY):

trafficserver/src/tscore/ink_queue.cc

Lines 268 to 280 in 5ef1036

	#ifdef SANITY
	if (result) {
	if (FREELIST_POINTER(item) == TO_PTR(FREELIST_POINTER(next))) {
	ink_abort("ink_freelist_new: loop detected");
	}
	if (((uintptr_t)(TO_PTR(FREELIST_POINTER(next)))) & 3) {
	ink_abort("ink_freelist_new: bad list");
	}
	if (TO_PTR(FREELIST_POINTER(next))) {
	dummy_forced_read(TO_PTR(FREELIST_POINTER(next)));
	}
	}
	#endif /* SANITY */