dm: core: Add dev_get_uclass_priv() to access uclass private data

Add a convenience function to access the private data that a uclass stores
for each of its devices. Convert over most existing uses for consistency
and to provide an example for others.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/gpio/sunxi_gpio.c b/drivers/gpio/sunxi_gpio.c
index 510123f..cf5c624 100644
--- a/drivers/gpio/sunxi_gpio.c
+++ b/drivers/gpio/sunxi_gpio.c
@@ -261,7 +261,7 @@
 static int gpio_sunxi_probe(struct udevice *dev)
 {
 	struct sunxi_gpio_platdata *plat = dev_get_platdata(dev);
-	struct gpio_dev_priv *uc_priv = dev->uclass_priv;
+	struct gpio_dev_priv *uc_priv = dev_get_uclass_priv(dev);
 
 	/* Tell the uclass how many GPIOs we have */
 	if (plat) {