drm/amd: Avoid BUG() for case of SRIOV missing IP version

No need to crash the kernel.  AMDGPU will now fail to probe.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>