hw/ptimer: Update .delta on period/freq change

Delta value must be updated on period/freq change, otherwise running timer
would be restarted (counter reloaded with old delta). Only m68k/mcf520x
and arm/arm_timer devices are currently doing freq change correctly, i.e.
stopping the timer. Perform delta update to fix affected devices and
eliminate potential further mistakes.
Signed-off-by: NDmitry Osipenko <digetx@gmail.com>
Reviewed-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: 4987ef5fdc128bb9a744fd794d3f609135c6a39c.1464367869.git.digetx@gmail.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/core/ptimer.c

@@ -190,6 +190,7 @@ void ptimer_stop(ptimer_state *s)
 /* Set counter increment interval in nanoseconds.  */
 void ptimer_set_period(ptimer_state *s, int64_t period)
 {
+    s->delta = ptimer_get_count(s);
     s->period = period;
     s->period_frac = 0;
     if (s->enabled) {
@@ -201,6 +202,7 @@ void ptimer_set_period(ptimer_state *s, int64_t period)
 /* Set counter frequency in Hz.  */
 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 {
+    s->delta = ptimer_get_count(s);
     s->period = 1000000000ll / freq;
     s->period_frac = (1000000000ll << 32) / freq;
     if (s->enabled) {