counter: Provide a wrapper to access device private data

For now this just wraps accessing struct counter_device::priv. However
this is about to change and converting drivers to this helper
individually makes fixing device lifetime issues result in easier to
review patches.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211230150300.72196-5-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/counter/counter-core.c

@@ -45,6 +45,18 @@ static struct bus_type counter_bus_type = {
 
 static dev_t counter_devt;
 
+/**
+ * counter_priv - access counter device private data
+ * @counter: counter device
+ *
+ * Get the counter device private data
+ */
+void *counter_priv(const struct counter_device *const counter)
+{
+	return counter->priv;
+}
+EXPORT_SYMBOL_GPL(counter_priv);
+
 /**
  * counter_register - register Counter to the system
  * @counter:	pointer to Counter to register

include/linux/counter.h

@@ -329,6 +329,8 @@ struct counter_device {
 	struct mutex ops_exist_lock;
 };
 
+void *counter_priv(const struct counter_device *const counter);
+
 int counter_register(struct counter_device *const counter);
 void counter_unregister(struct counter_device *const counter);
 int devm_counter_register(struct device *dev,