[GFS2] Make headers compile on their own

As per Jan Engelhardt's comments, this should make all the headers
compile on their own by including and/or declaring structures
early.

Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/ops_super.h b/fs/gfs2/ops_super.h
index cbc4f73..9de73f0 100644
--- a/fs/gfs2/ops_super.h
+++ b/fs/gfs2/ops_super.h
@@ -10,6 +10,8 @@
 #ifndef __OPS_SUPER_DOT_H__
 #define __OPS_SUPER_DOT_H__
 
+#include <linux/fs.h>
+
 extern struct super_operations gfs2_super_ops;
 
 #endif /* __OPS_SUPER_DOT_H__ */