md: remove the kernel version of md_u.h

mdp_major can just move to drivers/md/md.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 37315a3..6f8fff7 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -801,6 +801,7 @@ static inline void mddev_check_write_zeroes(struct mddev *mddev, struct bio *bio
 		mddev->queue->limits.max_write_zeroes_sectors = 0;
 }
 
+extern int mdp_major;
 void md_autostart_arrays(int part);
 
 #endif /* _MD_MD_H */