md: removing typedefs:  mdk_rdev_t -> struct md_rdev

The typedefs are just annoying. 'mdk' probably refers to 'md_k.h'
which used to be an include file that defined this thing.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index a3d5483..2377a46 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -4,7 +4,7 @@
 typedef struct mirror_info mirror_info_t;
 
 struct mirror_info {
-	mdk_rdev_t	*rdev;
+	struct md_rdev	*rdev;
 	sector_t	head_position;
 };