Fix BMM150 sensor initialization check

Author: qqqlab

src/mag/MagGizmoBMM150.h

@@ -25,7 +25,7 @@ class MagGizmoBMM150: public MagGizmo {
 
       //configure sensor
       BMM150_I2C *sensor = new BMM150_I2C(i2c, config->i2c_adr);
-      if(!sensor->begin()) {
+      if(sensor->begin() != 0) {
         Serial.printf("RDR: BMM150 init failed.\n");
         delete sensor;
         return nullptr;