drm/fb-helper: Add missed unlocks in setcmap_legacy()

setcmap_legacy() does not call drm_modeset_unlock_all() in some exits,
add the missed unlocks with goto to fix it.

Fixes: 964c6006 ("drm/fb-helper: separate the fb_setcmap helper into atomic and legacy paths")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201203144248.418281-1-hslester96@gmail.com

drivers/gpu/drm/drm_fb_helper.c

@@ -946,11 +946,15 @@ static int setcmap_legacy(struct fb_cmap *cmap, struct fb_info *info)
 	drm_modeset_lock_all(fb_helper->dev);
 	drm_client_for_each_modeset(modeset, &fb_helper->client) {
 		crtc = modeset->crtc;
-		if (!crtc->funcs->gamma_set || !crtc->gamma_size)
-			return -EINVAL;
+		if (!crtc->funcs->gamma_set || !crtc->gamma_size) {
+			ret = -EINVAL;
+			goto out;
+		}
 
-		if (cmap->start + cmap->len > crtc->gamma_size)
-			return -EINVAL;
+		if (cmap->start + cmap->len > crtc->gamma_size) {
+			ret = -EINVAL;
+			goto out;
+		}
 
 		r = crtc->gamma_store;
 		g = r + crtc->gamma_size;
@@ -963,8 +967,9 @@ static int setcmap_legacy(struct fb_cmap *cmap, struct fb_info *info)
 		ret = crtc->funcs->gamma_set(crtc, r, g, b,
 					     crtc->gamma_size, NULL);
 		if (ret)
-			return ret;
+			goto out;
 	}
+out:
 	drm_modeset_unlock_all(fb_helper->dev);
 
 	return ret;