HAL_Linux: cope with different I2C headers for data

libraries/AP_HAL_Linux/I2CDriver.cpp

@@ -13,6 +13,9 @@
 #include <linux/i2c-dev.h>
 #ifndef I2C_SMBUS_BLOCK_MAX
 #include <linux/i2c.h>
+#define I2C_DATA_TYPE __u8
+#else
+#define I2C_DATA_TYPE char
 #endif
 
 using namespace Linux;
@@ -142,13 +145,13 @@ uint8_t LinuxI2CDriver::readRegisters(uint8_t addr, uint8_t reg,
         addr  : addr,
         flags : 0,
         len   : 1,
-        buf   : (char *)&reg
+        buf   : (I2C_DATA_TYPE *)&reg
         },
         {
         addr  : addr,
         flags : I2C_M_RD,
         len   : len,
-        buf   : (char *)data,
+        buf   : (I2C_DATA_TYPE *)data,
         }
     };
     struct i2c_rdwr_ioctl_data i2c_data = {
@@ -179,11 +182,11 @@ uint8_t LinuxI2CDriver::readRegistersMultiple(uint8_t addr, uint8_t reg,
             msgs[i*2].addr = addr;
             msgs[i*2].flags = 0;
             msgs[i*2].len = 1;
-            msgs[i*2].buf = (char *)&reg;
+            msgs[i*2].buf = &reg;
             msgs[i*2+1].addr = addr;
             msgs[i*2+1].flags = I2C_M_RD;
             msgs[i*2+1].len = len;
-            msgs[i*2+1].buf = (char *)data;
+            msgs[i*2+1].buf = (I2C_DATA_TYPE *)data;
             data += len;
         };
         if (ioctl(_fd, I2C_RDWR, &i2c_data) == -1) {