QOM object instance should not modify its class state (because
all other objects instanciated from this class get affected).
Instead of modifying the PMBusDeviceClass 'device_num_pages' field
the first time a instance is initialized (in pmbus_pages_alloc),
introduce a new pmbus_pages_num() helper which returns the page
number from the class without modifying the class state.
The code logic become slighly simplified.
Inspired-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230523064408.57941-4-philmd@linaro.org>
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