drm: constify sysrq_key_op

With earlier commits, the API no longer discards the const-ness of the
sysrq_key_op. As such we can add the notation.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-kernel@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://lore.kernel.org/r/20200513214351.2138580-8-emil.l.velikov@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/drm_fb_helper.c

@@ -307,13 +307,13 @@ static void drm_fb_helper_sysrq(int dummy1)
 	schedule_work(&drm_fb_helper_restore_work);
 }
 
-static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = {
+static const struct sysrq_key_op sysrq_drm_fb_helper_restore_op = {
 	.handler = drm_fb_helper_sysrq,
 	.help_msg = "force-fb(V)",
 	.action_msg = "Restore framebuffer console",
 };
 #else
-static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { };
+static const struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { };
 #endif
 
 static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)