Fix type size for 16bit cpu

src/kservice.c

@@ -1221,7 +1221,7 @@ const rt_uint8_t __lowest_bit_bitmap[] =
  * @return return the index of the first bit set. If value is 0, then this function
  * shall return 0.
  */
-int __rt_ffs(int value)
+rt_ubase_t __rt_ffs(rt_ubase_t value)
 {
     if (value == 0) return 0;