drm/radeon: drm/radeon: add missing radeon_semaphore_free to error path

It would appear this bug has been copy/pasted many times without being noticed.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>