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.c b/drivers/md/linear.c
index 6cd2c31..0b5cac0 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -126,7 +126,7 @@
 static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
 {
 	linear_conf_t *conf;
-	mdk_rdev_t *rdev;
+	struct md_rdev *rdev;
 	int i, cnt;
 
 	conf = kzalloc (sizeof (*conf) + raid_disks*sizeof(dev_info_t),
@@ -213,7 +213,7 @@
 	return md_integrity_register(mddev);
 }
 
-static int linear_add(mddev_t *mddev, mdk_rdev_t *rdev)
+static int linear_add(mddev_t *mddev, struct md_rdev *rdev)
 {
 	/* Adding a drive to a linear array allows the array to grow.
 	 * It is permitted if the new drive has a matching superblock