drm/amdgpu: screen freeze and userq driver crash

Screen freeze and userq fence driver crash while playing Xonotic

v2: (Christian)
    - There is change that fence might signal in between testing
      and grabbing the lock. Hence we can move the lock above the
      if..else check and use the dma_fence_is_signaled_locked().

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