MPU6000: minor fixes

the hardware functions should be private, and cs_pin should be uint8_t

libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.cpp

@@ -64,7 +64,7 @@
 #define BIT_I2C_IF_DIS              0x10
 #define BIT_INT_STATUS_DATA   0x01
 
-int     AP_InertialSensor_MPU6000::_cs_pin;
+uint8_t AP_InertialSensor_MPU6000::_cs_pin;
 
 /* pch: by the data sheet, the gyro scale should be 16.4LSB per DPS
  *      Given the radians conversion factor (0.174532), the gyro scale factor
@@ -90,7 +90,7 @@ const uint8_t AP_InertialSensor_MPU6000::_temp_data_index = 3;
 
 static volatile uint8_t _new_data;
 
-AP_InertialSensor_MPU6000::AP_InertialSensor_MPU6000( int cs_pin )
+AP_InertialSensor_MPU6000::AP_InertialSensor_MPU6000( uint8_t cs_pin )
 {
   _cs_pin = cs_pin; /* can't use initializer list,  is static */
   _gyro.x = 0;

libraries/AP_InertialSensor/AP_InertialSensor_MPU6000.h

@@ -14,7 +14,7 @@ class AP_InertialSensor_MPU6000 : public AP_InertialSensor
 {
   public:
 
-  AP_InertialSensor_MPU6000( int cs_pin );
+  AP_InertialSensor_MPU6000( uint8_t cs_pin );
 
   void init( AP_PeriodicProcess * scheduler );
 
@@ -33,14 +33,14 @@ class AP_InertialSensor_MPU6000 : public AP_InertialSensor
   uint32_t sample_time();
   void reset_sample_time();
 
+  private:
+
   static void read(uint32_t);
   static void data_interrupt(void);
   static uint8_t register_read( uint8_t reg );
   static void register_write( uint8_t reg, uint8_t val );
   static void hardware_init();
 
-  private:
-
   Vector3f _gyro;
   Vector3f _accel;
   float _temp;
@@ -63,7 +63,7 @@ class AP_InertialSensor_MPU6000 : public AP_InertialSensor
   static int16_t _data[7];
 
   /* TODO deprecate _cs_pin */
-  static int _cs_pin;
+  static uint8_t _cs_pin;
 };
 
 #endif // __AP_INERTIAL_SENSOR_MPU6000_H__