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/bma180/bma180.cpp

@@ -238,7 +238,7 @@ BMA180::BMA180(int bus, spi_dev_e device) :
 	_reports(nullptr),
 	_accel_range_scale(0.0f),
 	_accel_range_m_s2(0.0f),
-	_accel_topic(-1),
+	_accel_topic(0),
 	_class_instance(-1),
 	_current_lowpass(0),
 	_current_range(0),
@@ -733,7 +733,7 @@ BMA180::measure()
 	poll_notify(POLLIN);
 
 	/* publish for subscribers */
-	if (_accel_topic > 0 && !(_pub_blocked))
+	if (_accel_topic != 0 && !(_pub_blocked))
 		orb_publish(ORB_ID(sensor_accel), _accel_topic, &report);
 
 	/* stop the perf counter */