drm: Constify drm_driver in drivers that don't modify it

A non-const structure containing function pointers is a possible attack
vector. The drm_driver structure is already const in most drivers, but
there are a few exceptions. Constify the structure in the drivers that
don't need to modify at, as a low-hanging fruit. The rest of the drivers
will need a more complex fix.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/arc/arcpgu_drv.c

@@ -145,7 +145,7 @@ static void arcpgu_debugfs_init(struct drm_minor *minor)
 }
 #endif
 
-static struct drm_driver arcpgu_drm_driver = {
+static const struct drm_driver arcpgu_drm_driver = {
 	.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_ATOMIC,
 	.name = "arcpgu",
 	.desc = "ARC PGU Controller",

drivers/gpu/drm/kmb/kmb_drv.c

@@ -400,7 +400,7 @@ static void kmb_irq_reset(struct drm_device *drm)
 
 DEFINE_DRM_GEM_CMA_FOPS(fops);
 
-static struct drm_driver kmb_driver = {
+static const struct drm_driver kmb_driver = {
 	.driver_features = DRIVER_GEM |
 	    DRIVER_MODESET | DRIVER_ATOMIC,
 	.irq_handler = kmb_isr,

drivers/gpu/drm/tdfx/tdfx_drv.c

@@ -56,7 +56,7 @@ static const struct file_operations tdfx_driver_fops = {
 	.llseek = noop_llseek,
 };
 
-static struct drm_driver driver = {
+static const struct drm_driver driver = {
 	.driver_features = DRIVER_LEGACY,
 	.fops = &tdfx_driver_fops,
 	.name = DRIVER_NAME,