Adapt the type used for adjtime_delta

clock_t is currently a signed type, but in NetBSD this is not the
case. As we plan on aligning our types we have to change this as this
prevents negative delta from being correctly used.

Change-Id: I9bccdee2b41626b0262471dc1900de505a1991a7

kernel/system/do_settime.c

@@ -17,7 +17,8 @@
  *===========================================================================*/
 int do_settime(struct proc * caller, message * m_ptr)
 {
-  clock_t newclock, ticks;
+  clock_t newclock;
+  int32_t ticks;
   time_t timediff;
   signed long long timediff_ticks;