drm/vmwgfx/vmwgfx_validation: Use flexible-array member instead of zero-length array

Suppresses the following coccinelle warning:

drivers/gpu/drm/vmwgfx/vmwgfx_validation.c:85:15-22: WARNING use flexible-array member instead
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323130204.45439-1-zou_wei@huawei.com

drivers/gpu/drm/vmwgfx/vmwgfx_validation.c

@@ -82,7 +82,7 @@ struct vmw_validation_res_node {
 	u32 reserved : 1;
 	u32 dirty : 1;
 	u32 dirty_set : 1;
-	unsigned long private[0];
+	unsigned long private[];
 };
 
 /**