[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_file.h b/fs/gfs2/ops_file.h
index b1c1bf8..ce319f8 100644
--- a/fs/gfs2/ops_file.h
+++ b/fs/gfs2/ops_file.h
@@ -9,6 +9,10 @@
 
 #ifndef __OPS_FILE_DOT_H__
 #define __OPS_FILE_DOT_H__
+
+#include <linux/fs.h>
+struct gfs2_inode;
+
 extern struct file gfs2_internal_file_sentinel;
 extern int gfs2_internal_read(struct gfs2_inode *ip,
 			      struct file_ra_state *ra_state,