speed up my_timer_init()

I run perf top during ./mtr testing and constantly see times()
function there. It's so slow, that it has no sense to run it
in a loop too many times.

This patch speeds up -suite=innodb for me from 218s to 208s.
9s of times() function!

mysys/my_rdtsc.c

@@ -812,7 +812,11 @@ void my_timer_init(MY_TIMER_INFO *mti)
     time1= my_timer_cycles();
     time2= my_timer_ticks();
     time3= time2; /* Avoids a Microsoft/IBM compiler warning */
+#if defined(HAVE_SYS_TIMES_H) && defined(HAVE_TIMES)
+    for (i= 0; i < 1000; ++i)
+#else
     for (i= 0; i < MY_TIMER_ITERATIONS * 1000; ++i)
+#endif
     {
       time3= my_timer_ticks();
       if (time3 - time2 > 10) break;