kobj: add comment and multiple inclusion protection

Signed-off-by: Robert P. J. Day <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

include/linux/kobj_map.h

···
+/*
+ * kobj_map.h
+ */
+
+#ifndef _KOBJ_MAP_H_
+#define _KOBJ_MAP_H_
+
 #include <linux/mutex.h>
 
 typedef struct kobject *kobj_probe_t(dev_t, int *, void *);
···
 void kobj_unmap(struct kobj_map *, dev_t, unsigned long);
 struct kobject *kobj_lookup(struct kobj_map *, dev_t, int *);
 struct kobj_map *kobj_map_init(kobj_probe_t *, struct mutex *);
+
+#endif /* _KOBJ_MAP_H_ */