platform: introduce OF style 'modalias' support for platform bus

Fix a problem that, the platform bus supports the OF style modalias
in .uevent() call, but not in its device 'modalias' sysfs attribute.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/include/linux/of_device.h b/include/linux/of_device.h
index 82ce324..8d7dd67 100644
--- a/include/linux/of_device.h
+++ b/include/linux/of_device.h
@@ -64,6 +64,12 @@
 static inline void of_device_uevent(struct device *dev,
 			struct kobj_uevent_env *env) { }
 
+static inline int of_device_get_modalias(struct device *dev,
+				   char *str, ssize_t len)
+{
+	return -ENODEV;
+}
+
 static inline int of_device_uevent_modalias(struct device *dev,
 				   struct kobj_uevent_env *env)
 {