of/i2c: implement of_find_i2c_adapter_by_node

This finds the struct i2c_adapter * for a given device tree node. Just
like of_find_i2c_device_by_node.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
diff --git a/include/linux/of_i2c.h b/include/linux/of_i2c.h
index 0efe8d4..1cb775f 100644
--- a/include/linux/of_i2c.h
+++ b/include/linux/of_i2c.h
@@ -20,6 +20,10 @@
 /* must call put_device() when done with returned i2c_client device */
 extern struct i2c_client *of_find_i2c_device_by_node(struct device_node *node);
 
+/* must call put_device() when done with returned i2c_adapter device */
+extern struct i2c_adapter *of_find_i2c_adapter_by_node(
+						struct device_node *node);
+
 #else
 static inline void of_i2c_register_devices(struct i2c_adapter *adap)
 {