drm/radeon: only save UVD bo when we have open handles

commit 4ad9c1c774c2af152283f510062094e768876f55 upstream.

Otherwise just reinitialize from scratch on resume,
and so make it more likely to succeed.

v2: rebased for 3.10-stable tree

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