lsm9ds1_mag: cleanup + consistency with other drivers

src/drivers/magnetometer/lsm9ds1_mag/LSM9DS1_MAG.cpp

@@ -68,20 +68,22 @@ int LSM9DS1_MAG::probe()
 	return PX4_ERROR;
 }
 
-bool LSM9DS1_MAG::Init()
+int LSM9DS1_MAG::init()
 {
-	if (SPI::init() != PX4_OK) {
+	int ret = SPI::init();
-		return false;
+
+	if (ret != PX4_OK) {
+		return ret;
 	}
 
 	if (!Reset()) {
 		PX4_ERR("reset failed");
-		return false;
+		return PX4_ERROR;
 	}
 
 	Start();
 
-	return true;
+	return PX4_OK;
 }
 
 bool LSM9DS1_MAG::Reset()
@@ -147,16 +149,9 @@ void LSM9DS1_MAG::RegisterClearBits(Register reg, uint8_t clearbits)
 
 void LSM9DS1_MAG::Start()
 {
-	Stop();
-
 	ScheduleOnInterval(1000000 / ST_LSM9DS1_MAG::M_ODR / 2);
 }
 
-void LSM9DS1_MAG::Stop()
-{
-	ScheduleClear();
-}
-
 void LSM9DS1_MAG::RunImpl()
 {
 	perf_count(_interval_perf);

src/drivers/magnetometer/lsm9ds1_mag/LSM9DS1_MAG.hpp

@@ -63,9 +63,9 @@ public:
 
 	void print_status();
 
-	bool Init();
+	int init() override;
+
 	void Start();
-	void Stop();
 	bool Reset();
 
 	void     RunImpl();

src/drivers/magnetometer/lsm9ds1_mag/lsm9ds1_mag_main.cpp

@@ -58,7 +58,7 @@ I2CSPIDriverBase *LSM9DS1_MAG::instantiate(const BusCLIArguments &cli, const Bus
 		return nullptr;
 	}
 
-	if (!instance->Init()) {
+	if (OK != instance->init()) {
 		delete instance;
 		return nullptr;
 	}