dma-buf: fix kernel-doc warning in <linux/dma-buf.h>

Fix kernel-doc warning in <linux/dma-buf.h>:

../include/linux/dma-buf.h:330: warning: Function parameter or member 'name_lock' not described in 'dma_buf'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/388523/Signed-off-by: Christian König <christian.koenig@amd.com>

include/linux/dma-buf.h

@@ -283,6 +283,7 @@ struct dma_buf_ops {
  * @exp_name: name of the exporter; useful for debugging.
  * @name: userspace-provided name; useful for accounting and debugging,
  *        protected by @resv.
+ * @name_lock: spinlock to protect name access
  * @owner: pointer to exporter module; used for refcounting when exporter is a
  *         kernel module.
  * @list_node: node for dma_buf accounting and debugging.
@@ -311,7 +312,7 @@ struct dma_buf {
 	void *vmap_ptr;
 	const char *exp_name;
 	const char *name;
-	spinlock_t name_lock; /* spinlock to protect name access */
+	spinlock_t name_lock;
 	struct module *owner;
 	struct list_head list_node;
 	void *priv;