drm/amd/amdgpu: make afmt_init cleanup if alloc fails (DCEv8)

If the allocation fails free memory and return error code.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>