drm/amdgpu: fix and cleanup user fence handling v2

We leaked the BO in the error pass, additional to that we only have
one user fence for all IBs in a job.

v2: remove white space changes

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