drm/amdgpu: Fix missing mca debugfs node

Use amdgpu_ip_version() helper function to check ip version.

The ip version contains other information,
use the helper function to avoid reading wrong value.

Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>