[bsp/at32] fixed auto check error

bsp/at32/libraries/rt_drivers/drv_gpio.c

@@ -260,10 +260,10 @@ static void at32_pin_mode(rt_device_t dev, rt_base_t pin, rt_uint8_t mode)
 
 rt_inline rt_int32_t bit2bitno(rt_uint32_t bit)
 {
-    int i;
+    rt_int32_t i;
     for (i = 0; i < 32; i++)
     {
-        if ((0x01 << i) == bit)
+        if (((rt_uint32_t)0x01 << i) == bit)
         {
             return i;
         }