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/linear.h b/drivers/md/linear.h
index 2f2da05..367967a 100644
--- a/drivers/md/linear.h
+++ b/drivers/md/linear.h
@@ -2,7 +2,7 @@
 #define _LINEAR_H
 
 struct dev_info {
-	mdk_rdev_t	*rdev;
+	struct md_rdev	*rdev;
 	sector_t	end_sector;
 };