drm/amd/display: Fix memory leak reported by coverity

Free memory allocated if any of the previous allocations failed.

>>>     CID 1487129:  Resource leaks  (RESOURCE_LEAK)
>>>     Variable "vpg" going out of scope leaks the storage it points to.

Addresses-Coverity-ID: 1487129: ("Resource leaks")

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>