drm/amdgpu: fix logic inversion in check

We probably never trigger this, but the logic inside the check is
inverted.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>