target-s390x: simplify SCKC helper

The clock comparator and the QEMU timer work the same way, triggering
at a given time, they just differ by the origin and the scale. It is
therefore possible to go from one to another without using the current
clock value. This spares two calls to qemu_clock_get_ns, which probably
return slightly different values, possibly reducing the accuracy.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NAlexander Graf <agraf@suse.de>

target-s390x/misc_helper.c

@@ -291,12 +291,13 @@ void HELPER(sckc)(CPUS390XState *env, uint64_t time)
         return;
     }
 
-    /* difference between now and then */
-    time -= clock_value(env);
+    /* difference between origins */
+    time -= env->tod_offset;
+
     /* nanoseconds */
     time = tod2time(time);
 
-    timer_mod(env->tod_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + time);
+    timer_mod(env->tod_timer, env->tod_basetime + time);
 }
 
 /* Store Clock Comparator */