drm/bridge/lontium-lt9611uxc: fix get_edid return code

Return NULL pointer from get_edid() callback rather than ERR_PTR()
pointer, as DRM code does NULL checks rather than IS_ERR(). Also while
we are at it, return NULL if getting EDID timed out.

Signed-off-by: Dmitry Baryshkov <[e-mail]>
Fixes: 0cbbd5b1a012 ("drm: bridge: add support for lontium LT9611UXC bridge")
Reviewed-by: Bjorn Andersson <[e-mail]>
Reviewed-by: Andrzej Hajda <[e-mail]>
Signed-off-by: Andrzej Hajda <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/bridge/lontium-lt9611uxc.c

···
 	ret = lt9611uxc_wait_for_edid(lt9611uxc);
 	if (ret < 0) {
 		dev_err(lt9611uxc->dev, "wait for EDID failed: %d\n", ret);
-		return ERR_PTR(ret);
+		return NULL;
+	} else if (ret == 0) {
+		dev_err(lt9611uxc->dev, "wait for EDID timeout\n");
+		return NULL;
 	}
 
 	return drm_do_get_edid(connector, lt9611uxc_get_edid_block, lt9611uxc);