drm/udl: dma-buf: Constify dma_buf_ops structures.

dma_buf_ops are not supposed to change at runtime. All functions
working with dma_buf_ops provided by <linux/dma-buf.h> work with
const dma_buf_ops. So mark the non-const structs as const.

File size before:
text data bss dec hex filename
2002 112 0 2114 842 drivers/gpu/drm/udl/udl_dmabuf.o

File size After adding 'const':
text data bss dec hex filename
2114 0 0 2114 842 drivers/gpu/drm/udl/udl_dmabuf.o

Signed-off-by: Arvind Yadav <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/cb4dfac[e-mail]

drivers/gpu/drm/udl/udl_dmabuf.c

···
 	return -EINVAL;
 }
 
-static struct dma_buf_ops udl_dmabuf_ops = {
+static const struct dma_buf_ops udl_dmabuf_ops = {
 	.attach			= udl_attach_dma_buf,
 	.detach			= udl_detach_dma_buf,
 	.map_dma_buf		= udl_map_dma_buf,