drm/radeon: activate UVD clocks before sending the destroy msg

commit c154a76311293f9671439286834aa325b7ef59fe upstream.

Make sure the UVD clocks are still active before sending
the destroy message, otherwise the hw might hang.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>