drm/amdgpu: resolve erroneous gfx_v9_4_2 prints

resolve bug on aldebaran where gfx error counts will
print on driver load when there are no errors present

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>