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/multipath.h b/drivers/md/multipath.h
index 3c5a45e..034f838 100644
--- a/drivers/md/multipath.h
+++ b/drivers/md/multipath.h
@@ -2,7 +2,7 @@
 #define _MULTIPATH_H
 
 struct multipath_info {
-	mdk_rdev_t	*rdev;
+	struct md_rdev	*rdev;
 };
 
 struct multipath_private_data {