hw/clock: Let clock_set_mul_div() return a boolean value

Let clock_set_mul_div() return a boolean value whether the
clock has been updated or not, similarly to clock_set().

Return early when clock_set_mul_div() is called with
same mul/div values the clock has.

Acked-by: Luc Michel <luc@lmichel.fr>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20240325152827.73817-2-philmd@linaro.org>

docs/devel/clocks.rst

@@ -279,6 +279,10 @@ You can change the multiplier and divider of a clock at runtime,
 so you can use this to model clock controller devices which
 have guest-programmable frequency multipliers or dividers.
 
+Similary to ``clock_set()``, ``clock_set_mul_div()`` returns ``true`` if
+the clock state was modified; that is, if the multiplier or the diviser
+or both were changed by the call.
+
 Note that ``clock_set_mul_div()`` does not automatically call
 ``clock_propagate()``. If you make a runtime change to the
 multiplier or divider you must call clock_propagate() yourself.