extensive orb_advert_t fixes

The calls to orb_advertise were being mishandled throughout the code.
There were ::close() calls on memory pointers, there were checks
against < 0 when it is a pointer to a object and values larger than
0x7ffffffff are valid. Some places orb_advert_t variables were
being initialized as 0 other places as -1.

The orb_advert_t type was changed to uintptr_t so the pointer value
would not be wrapped as a negative number. This was causing a failure
on ARM.

Tests for < 0 were changed to == 0 since a null pointer is the valid
representation for error, or uninitialized.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/platforms/posix/drivers/barosim/baro.cpp

@@ -213,7 +213,7 @@ BAROSIM::BAROSIM(device::Device *interface, barosim::prom_u &prom_buf, const cha
 	_OFF(0),
 	_SENS(0),
 	_msl_pressure(101325),
-	_baro_topic(-1),
+	_baro_topic(0),
 	_orb_class_instance(-1),
 	_class_instance(-1),
 	_sample_perf(perf_alloc(PC_ELAPSED, "barosim_read")),
@@ -315,7 +315,7 @@ BAROSIM::init()
 		_baro_topic = orb_advertise_multi(ORB_ID(sensor_baro), &brp,
 				&_orb_class_instance, (is_external()) ? ORB_PRIO_HIGH : ORB_PRIO_DEFAULT);
 
-		if (_baro_topic == (orb_advert_t)(-1)) {
+		if (_baro_topic == 0) {
 			PX4_ERR("failed to create sensor_baro publication");
 		}
 		//PX4_WARN("sensor_baro publication %ld", _baro_topic);
@@ -722,7 +722,7 @@ BAROSIM::collect()
 
 		/* publish it */
 		if (!(_pub_blocked)) {
-			if (_baro_topic != (orb_advert_t)(-1)) {
+			if (_baro_topic != 0) {
 				/* publish it */
 				orb_publish(ORB_ID(sensor_baro), _baro_topic, &report);
 			}