of/i2c: add dummy inline functions for when CONFIG_OF_I2C(_MODULE) isn't defined

If CONFIG_OF_I2C and CONFIG_OF_I2C_MODULE are undefined no declaration of
of_find_i2c_device_by_node and of_find_i2c_adapter_by_node will be
available. Add dummy inline functions to avoid compilation breakage.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

include/linux/of_i2c.h

@@ -29,6 +29,18 @@ static inline void of_i2c_register_devices(struct i2c_adapter *adap)
 {
 	return;
 }
+
+static inline struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
+{
+	return NULL;
+}
+
+/* must call put_device() when done with returned i2c_adapter device */
+static inline struct i2c_adapter *of_find_i2c_adapter_by_node(
+						struct device_node *node)
+{
+	return NULL;
+}
 #endif /* CONFIG_OF_I2C */
 
 #endif /* __LINUX_OF_I2C_H */