drm/fb-helper: Remove test for fb_dirty callback from deferred-I/O helper

The helper for processing deferred I/O on pages has no dependency on
the fb_dirty damge-handling callback; so remove the test. In practice,
deferred I/O is only used with damage handling and the damage worker
already guarantees the presence of the fb_dirty callback.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20221115115819.23088-4-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -656,17 +656,15 @@ void drm_fb_helper_deferred_io(struct fb_info *info, struct list_head *pagerefli
 		min_off = min(min_off, start);
 		max_off = max(max_off, end);
 	}
-	if (min_off >= max_off)
-		return;
 
-	if (helper->funcs->fb_dirty) {
-		/*
-		 * As we can only track pages, we might reach beyond the end
-		 * of the screen and account for non-existing scanlines. Hence,
-		 * keep the covered memory area within the screen buffer.
-		 */
-		max_off = min(max_off, info->screen_size);
+	/*
+	 * As we can only track pages, we might reach beyond the end
+	 * of the screen and account for non-existing scanlines. Hence,
+	 * keep the covered memory area within the screen buffer.
+	 */
+	max_off = min(max_off, info->screen_size);
 
+	if (min_off < max_off) {
 		drm_fb_helper_memory_range_to_clip(info, min_off, max_off - min_off, &damage_area);
 		drm_fb_helper_damage(helper, damage_area.x1, damage_area.y1,
 				     drm_rect_width(&damage_area),