drm/amdgpu: fix an error code in init_pmu_entry_by_type_and_add()

If the kmemdup() fails then this should return a negative error code
but it currently returns success

Fixes: b4a7db71

 ("drm/amdgpu: add per device user friendly xgmi events for vega20")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>