Fix build on macOS

utils.c:49:9: error: use of undeclared identifier 'mach_clk'

utils.c

@@ -46,7 +46,7 @@ static uint64_t semu_timer_clocksource(uint64_t freq)
     return t.tv_sec * freq + mult_frac(t.tv_nsec, freq, 1e9);
 #elif defined(HAVE_MACH_TIMER)
     static mach_timebase_info_data_t t;
-    if (mach_clk.denom == 0)
+    if (t.denom == 0)
         (void) mach_timebase_info(&t);
     return mult_frac(mach_absolute_time() * freq, t.numer, t.denom);
 #else
@@ -62,4 +62,4 @@ uint64_t semu_timer_get(semu_timer_t *timer)
 void semu_timer_rebase(semu_timer_t *timer, uint64_t time)
 {
     timer->begin = semu_timer_clocksource(timer->freq) - time;
-}
+}