ppc: Remove a potential overflow in muldiv64()

The coccinelle script:
scripts/coccinelle/overflow_muldiv64.cocci
gives us a list of potential overflows in muldiv64()
(the two first parameters are 64bit values).

This patch fixes one, as the fix seems obvious:

replace muldiv64(a, b, c) by muldiv64(b, a, c)
as "a" and "b" are 64bit values but a <= NANOSECONDS_PER_SECOND.
(10^9 -> 30bit value).
Signed-off-by: NLaurent Vivier <lvivier@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/ppc/ppc.c

@@ -880,7 +880,7 @@ static int timebase_post_load(void *opaque, int version_id)
     host_ns = qemu_clock_get_ns(QEMU_CLOCK_HOST);
     ns_diff = MAX(0, host_ns - tb_remote->time_of_the_day_ns);
     migration_duration_ns = MIN(NANOSECONDS_PER_SECOND, ns_diff);
-    migration_duration_tb = muldiv64(migration_duration_ns, freq,
+    migration_duration_tb = muldiv64(freq, migration_duration_ns,
                                      NANOSECONDS_PER_SECOND);
     guest_tb = tb_remote->guest_timebase + MIN(0, migration_duration_tb);