drm_plane_helper_funcs and drm_plane_funcsare not supposed to change
at runtime. All functions working with drm_plane_helper_funcs and
drm_plane_funcs work with const. So mark the non-const structs as const.
File size before:
   text	   data	    bss	    dec	    hex	filename
   6072	    596	      0	   6668	   1a0c atmel_hlcdc_plane.o
File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   6218	    436	      0	   6654	   19fe atmel_hlcdc_plane.o
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/646415a3b2e62182f85254115e8491e5caf4b2c7.1499098826.git.arvind.yadav.cs@gmail.com
 
                        desc->name);
 }
 
-static struct drm_plane_helper_funcs atmel_hlcdc_layer_plane_helper_funcs = {
+static const struct drm_plane_helper_funcs atmel_hlcdc_layer_plane_helper_funcs = {
        .atomic_check = atmel_hlcdc_plane_atomic_check,
        .atomic_update = atmel_hlcdc_plane_atomic_update,
        .atomic_disable = atmel_hlcdc_plane_atomic_disable,
        kfree(state);
 }
 
-static struct drm_plane_funcs layer_plane_funcs = {
+static const struct drm_plane_funcs layer_plane_funcs = {
        .update_plane = drm_atomic_helper_update_plane,
        .disable_plane = drm_atomic_helper_disable_plane,
        .set_property = drm_atomic_helper_plane_set_property,