md: rename "mdk_personality" to "md_personality"

"mdk" doesn't mean anything any more.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index 38a9012ff..0eb08a4 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -670,7 +670,7 @@
 {
 }
 
-static struct mdk_personality raid0_personality=
+static struct md_personality raid0_personality=
 {
 	.name		= "raid0",
 	.level		= 0,