fixed compiling error, RT_Device_Class_I2C is not defined in rtdef.h

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2173 bbd45198-f89e-11dd-88c7-29a3b14d5316

bsp/efm32/drv_iic.c

@@ -609,7 +609,7 @@ rt_err_t rt_hw_iic_register(
         RT_ASSERT(0);
     }
 
-    device->type        = RT_Device_Class_I2C;
+    device->type        = RT_Device_Class_Unknown;
     device->rx_indicate = RT_NULL;
     device->tx_complete = RT_NULL;
     device->init        = rt_iic_init;