qemu: aspeed_timer: Use signed muldiv for timer resets

If the host decrements the counter register that results in a negative
delta. This is then passed to muldiv64 which only handles unsigned
numbers resulting in bogus results.

This fix ensures the data being operated on is signed before it is
ultimately casted to the final unsigned value.

Test case: kexec a kernel using aspeed_timer and it will freeze on the
second bootup when the kernel initializes the timer. With this patch
that no longer happens and the timer appears to run OK.

Signed-off-by: Christian Svensson <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>

hw/timer/aspeed_timer.c

@@ -253,7 +253,7 @@ static void aspeed_timer_set_value(AspeedTimerCtrlState *s, int timer, int reg,
             int64_t delta = (int64_t) value - (int64_t) calculate_ticks(t, now);
             uint32_t rate = calculate_rate(t);
 
-            t->start += muldiv64(delta, NANOSECONDS_PER_SECOND, rate);
+            t->start = (int64_t)t->start + ((__int128_t)delta * NANOSECONDS_PER_SECOND / rate);
             aspeed_timer_mod(t);
         }
         break;