drm: Constify struct drm_fb_helper_funcs

There's no need for this to be modifiable. Make it const so that it can
be put into the .rodata section.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/gma500/framebuffer.c b/drivers/gpu/drm/gma500/framebuffer.c
index e7fcc14..76e4d77 100644
--- a/drivers/gpu/drm/gma500/framebuffer.c
+++ b/drivers/gpu/drm/gma500/framebuffer.c
@@ -561,7 +561,7 @@
 	return psbfb_create(psb_fbdev, sizes);
 }
 
-static struct drm_fb_helper_funcs psb_fb_helper_funcs = {
+static const struct drm_fb_helper_funcs psb_fb_helper_funcs = {
 	.gamma_set = psbfb_gamma_set,
 	.gamma_get = psbfb_gamma_get,
 	.fb_probe = psbfb_probe,