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/drivers/airspeed/airspeed.cpp

@@ -86,8 +86,8 @@ Airspeed::Airspeed(int bus, int address, unsigned conversion_interval, const cha
 	_measure_ticks(0),
 	_collect_phase(false),
 	_diff_pres_offset(0.0f),
-	_airspeed_pub(-1),
-	_subsys_pub(-1),
+	_airspeed_pub(0),
+	_subsys_pub(0),
 	_class_instance(-1),
 	_conversion_interval(conversion_interval),
 	_sample_perf(perf_alloc(PC_ELAPSED, "airspeed_read")),
@@ -146,7 +146,7 @@ Airspeed::init()
 		/* measurement will have generated a report, publish */
 		_airspeed_pub = orb_advertise(ORB_ID(differential_pressure), &arp);
 
-		if (_airspeed_pub < 0)
+		if (_airspeed_pub == 0)
 			warnx("uORB started?");
 	}
 
@@ -367,7 +367,7 @@ Airspeed::update_status()
 			SUBSYSTEM_TYPE_DIFFPRESSURE
 		};
 
-		if (_subsys_pub > 0) {
+		if (_subsys_pub == 0) {
 			orb_publish(ORB_ID(subsystem_info), _subsys_pub, &info);
 		} else {
 			_subsys_pub = orb_advertise(ORB_ID(subsystem_info), &info);