sandbox: Update the VBE firmware location

The image size was increased but the firmware-update part was not
updated. Correct this so that VBE firmware update can succeed with
sandbox_vpl.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 85c66dc95c2 ("sandbox: Expand size for VPL image")
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index d72d7a5..7c1ee71 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -129,7 +129,7 @@
 			status = "disabled";
 			compatible = "fwupd,vbe-simple";
 			storage = "mmc3";
-			skip-offset = <0x400000>;
+			skip-offset = <0x800000>;
 			area-start = <0>;
 			area-size = <0xe00000>;
 			state-offset = <0xdffc00>;