driver-core: add include guard to linux/container.h

Add a header include guard just in case.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20190819071606.10965-1-yamada.masahiro@socionext.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/container.h

@@ -6,6 +6,9 @@
  * Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
  */
 
+#ifndef _LINUX_CONTAINER_H
+#define _LINUX_CONTAINER_H
+
 #include <linux/device.h>
 
 /* drivers/base/power/container.c */
@@ -20,3 +23,5 @@ static inline struct container_dev *to_container_dev(struct device *dev)
 {
 	return container_of(dev, struct container_dev, dev);
 }
+
+#endif /* _LINUX_CONTAINER_H */