[PATCH 3/3] hw/i2c/pmbus_device: Fix modifying QOM class internals from instance

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

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>
---
 hw/i2c/pmbus_device.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/hw/i2c/pmbus_device.c b/hw/i2c/pmbus_device.c
index 44fe4eddbb..8bc9d5108a 100644
--- a/hw/i2c/pmbus_device.c
+++ b/hw/i2c/pmbus_device.c
@@ -190,15 +190,18 @@ static void pmbus_quick_cmd(SMBusDevice *smd, uint8_t read)
     }
 }
 
+static uint8_t pmbus_pages_num(PMBusDevice *pmdev)
+{
+    const PMBusDeviceClass *k = PMBUS_DEVICE_GET_CLASS(pmdev);
+
+    /* some PMBus devices don't use the PAGE command, so they get 1 page */
+    return k->device_num_pages ? : 1;
+}
+
 static void pmbus_pages_alloc(PMBusDevice *pmdev)
 {
-    /* some PMBus devices don't use the PAGE command, so they get 1 page */
-    PMBusDeviceClass *k = PMBUS_DEVICE_GET_CLASS(pmdev);
-    if (k->device_num_pages == 0) {
-        k->device_num_pages = 1;
-    }
-    pmdev->num_pages = k->device_num_pages;
-    pmdev->pages = g_new0(PMBusPage, k->device_num_pages);
+    pmdev->num_pages = pmbus_pages_num(pmdev);
+    pmdev->pages = g_new0(PMBusPage, pmdev->num_pages);
 }
 
 void pmbus_check_limits(PMBusDevice *pmdev)
-- 
2.38.1