drm/amdgpu: Adjust debugfs register access permissions

Regular users shouldn't have read access.

Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit c0cfd2e652553d607b910be47d0cc5a7f3a78641)
Cc: stable@vger.kernel.org
1 file changed