Fix legacy __rt_ffs_tiny()

Some compiler complains value & (value - 1) ^ value
better (value & (value - 1)) ^ value

src/kservice.c

@@ -1092,7 +1092,7 @@ const rt_uint8_t __lowest_bit_bitmap[] =
  */
 int __rt_ffs(int value)
 {
-    return __lowest_bit_bitmap[(rt_uint32_t)(value & (value - 1) ^ value) % 37];
+    return __lowest_bit_bitmap[(rt_uint32_t)((value & (value - 1)) ^ value) % 37];
 }
 #else
 const rt_uint8_t __lowest_bit_bitmap[] =