md: move md_k.h from include/linux/raid/ to drivers/md/

It really is nicer to keep related code together..

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index 64e4c77..3d06df8 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -19,8 +19,8 @@
 */
 
 #include <linux/blkdev.h>
-#include <linux/raid/md_k.h>
 #include <linux/seq_file.h>
+#include "md.h"
 #include "raid0.h"
 
 static void raid0_unplug(struct request_queue *q)