of: add helper function to retrive match data

It's a common operation for device drivers to retrive the data
member from of_device_id struct in their probe function.

Most driver end up doing:
    const struct of_device_id *match;
    match = of_match_device(driver_of_match, &pdev->dev);
    driver->data = match->data;

With the of_device_get_match_data helper function all this can
done in one go.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
[robh: add missing inline to dummmy declaration]
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/device.c

@@ -163,6 +163,18 @@ void of_device_unregister(struct platform_device *ofdev)
 }
 EXPORT_SYMBOL(of_device_unregister);
 
+const void *of_device_get_match_data(const struct device *dev)
+{
+	const struct of_device_id *match;
+
+	match = of_match_device(dev->driver->of_match_table, dev);
+	if (!match)
+		return NULL;
+
+	return match->data;
+}
+EXPORT_SYMBOL(of_device_get_match_data);
+
 ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len)
 {
 	const char *compat;