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/l3gd20/l3gd20.cpp

@@ -411,7 +411,7 @@ L3GD20::L3GD20(int bus, const char* path, spi_dev_e device, enum Rotation rotati
 	_gyro_scale{},
 	_gyro_range_scale(0.0f),
 	_gyro_range_rad_s(0.0f),
-	_gyro_topic(-1),
+	_gyro_topic(0),
 	_orb_class_instance(-1),
 	_class_instance(-1),
 	_current_rate(0),
@@ -490,7 +490,7 @@ L3GD20::init()
 	_gyro_topic = orb_advertise_multi(ORB_ID(sensor_gyro), &grp,
 		&_orb_class_instance, (is_external()) ? ORB_PRIO_VERY_HIGH : ORB_PRIO_DEFAULT);
 
-	if (_gyro_topic < 0) {
+	if (_gyro_topic == 0) {
 		debug("failed to create sensor_gyro publication");
 	}