drm/kms: fix fb cmap allocation to use modeset->crtc not crtc

crtc may be undefined at this point.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 515b838..9a0aac0 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -908,7 +908,7 @@
 
 	if (new_fb) {
 		info->var.pixclock = 0;
-		ret = fb_alloc_cmap(&info->cmap, crtc->gamma_size, 0);
+		ret = fb_alloc_cmap(&info->cmap, modeset->crtc->gamma_size, 0);
 		if (ret)
 			return ret;
 		if (register_framebuffer(info) < 0) {