ocfs2: fix a GCC warning

Fix the following compile warning:

fs/ocfs2/dlmglue.c:99:30: warning: �lockdep_keys� defined but not used [-Wunused-variable]
 static struct lock_class_key lockdep_keys[OCFS2_NUM_LOCK_TYPES];

Link: http://lkml.kernel.org/r/1536938148-32110-1-git-send-email-zhongjiang@huawei.com
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ocfs2/dlmglue.c

@@ -96,7 +96,9 @@ struct ocfs2_unblock_ctl {
 };
 
 /* Lockdep class keys */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key lockdep_keys[OCFS2_NUM_LOCK_TYPES];
+#endif
 
 static int ocfs2_check_meta_downconvert(struct ocfs2_lock_res *lockres,
 					int new_level);