drm/amdgpu: free hw_vm_fence when fail in amdgpu_job_alloc

drm/amdgpu: free hw_vm_fence when fail in amdgpu_job_alloc

If drm_sched_job_init fails, hw_vm_fence is not freed currently,
then cause memory leak.

Fixes: db36632ea51e ("drm/amdgpu: clean up and unify hw fence handling")
Link: https://lore.kernel.org/amd-gfx/a5a828cb-0e4a-41f0-94c3-df31e5ddad52@amd.com/T/#t
Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
Reviewed-by: Amos Kong <kongjianjun@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>