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>