tests/functional: Fix URL of gb200nvl-bmc image

Commit [1] moved the FW image of the gb200nvl-bmc machine and broke
the associated functional test. Fix that.

[1] 52451b2472

Cc: Ed Tanous <etanous@nvidia.com>
Cc: Patrick Williams <patrick@stwcx.xyz>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20251222073351.166720-1-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

tests/functional/arm/test_aspeed_gb200nvl_bmc.py

@@ -11,7 +11,7 @@ from aspeed import AspeedTest
 class GB200Machine(AspeedTest):
 
     ASSET_GB200_FLASH = Asset(
-        'https://github.com/legoater/qemu-aspeed-boot/raw/refs/heads/master/images/gb200nvl-obmc/obmc-phosphor-image-gb200nvl-obmc-20250702182348.static.mtd.xz',
+        'https://github.com/legoater/qemu-aspeed-boot/raw/refs/heads/master/images/gb200nvl-bmc/openbmc-20250702182348/obmc-phosphor-image-gb200nvl-obmc-20250702182348.static.mtd.xz',
         'b84819317cb3dc762895ad507705978ef000bfc77c50c33a63bdd37921db0dbc')
 
     def test_arm_aspeed_gb200_openbmc(self):