[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>

fs/gfs2/util.h

@@ -10,6 +10,7 @@
 #ifndef __UTIL_DOT_H__
 #define __UTIL_DOT_H__
 
+#include "incore.h"
 
 #define fs_printk(level, fs, fmt, arg...) \
 	printk(level "GFS2: fsid=%s: " fmt , (fs)->sd_fsname , ## arg)