lava: amd64-upsquared6000: Use weekly image on v2022 1st stage

Commit 160e8737 ("lava: amd64-upsquared6000: Use v2022 1st stage image
with firmware pkgs") set the UP Squared 6000 1st stage image to a daily
build as it included the required firmware pkgs. As the daily image will
get deleted soon, let's use a weekly one until the next v2022 release it
out.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>

lava/devices.yaml

@@ -8,7 +8,7 @@ device-amd64-upsquared6000:
         - boot
       deploy_device: emmc
       device_type: aaeon-UPN-EHLX4RE-A10-0864
-      firststageurl: "https://images.apertis.org/daily/v2022/20220829.0116"
+      firststageurl: "https://images.apertis.org/weekly/v2022/20220831.0116"
       needs_dtb: false
 device-armhf-imx6-sabrelite:
       arch: armhf