md: proper extern for mdp_major

This patch adds a proper extern for mdp_major in include/linux/raid/md.h

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/raid/md.h b/include/linux/raid/md.h
index 81a1a02..b7386ae 100644
--- a/include/linux/raid/md.h
+++ b/include/linux/raid/md.h
@@ -72,6 +72,8 @@
  */
 #define MD_PATCHLEVEL_VERSION           3
 
+extern int mdp_major;
+
 extern int register_md_personality (struct mdk_personality *p);
 extern int unregister_md_personality (struct mdk_personality *p);
 extern mdk_thread_t * md_register_thread (void (*run) (mddev_t *mddev),