dlm: Change rwlock which is only used in write mode to a spinlock

The ls_dirtbl[].lock was an rwlock, but since it was only used in write
mode a spinlock will suffice.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h
index 076e86f..d01ca0a 100644
--- a/fs/dlm/dlm_internal.h
+++ b/fs/dlm/dlm_internal.h
@@ -99,7 +99,7 @@
 
 struct dlm_dirtable {
 	struct list_head	list;
-	rwlock_t		lock;
+	spinlock_t		lock;
 };
 
 struct dlm_rsbtable {