AP_InertialSensor: fixed some compiler warnings

libraries/AP_InertialSensor/AP_InertialSensor.cpp

@@ -184,6 +184,8 @@ AP_InertialSensor::_init_gyro()
         float diff_norm[INS_MAX_INSTANCES];
         uint8_t i;
 
+        memset(diff_norm, 0, sizeof(diff_norm));
+
         hal.console->print_P(PSTR("*"));
 
         for (uint8_t k=0; k<num_gyros; k++) {
@@ -261,6 +263,9 @@ AP_InertialSensor::_init_accel()
     float total_change[INS_MAX_INSTANCES];
     float max_offset[INS_MAX_INSTANCES];
 
+    memset(max_offset, 0, sizeof(max_offset));
+    memset(total_change, 0, sizeof(total_change));
+
     // cold start
     hal.scheduler->delay(100);