Fix fifo overflow correction.

src/common/tusb_fifo.c

@@ -342,7 +342,7 @@ static uint16_t backward_pointer(tu_fifo_t* f, uint16_t p, uint16_t offset)
   // We limit the index space of p such that a correct wrap around happens
   // Check for a wrap around or if we are in unused index space - This has to be checked first!!
   // We are exploiting the wrap around to the correct index
-  if ((p < p - offset) || (p - offset > f->max_pointer_idx))
+  if ((p < (uint16_t)(p - offset)) || ((uint16_t)(p - offset) > f->max_pointer_idx))
   {
     p = (p - offset) - f->non_used_index_space;
   }