drm/amdgpu: Make amdgpu_fence_emit() non-failing v2

drm/amdgpu: Make amdgpu_fence_emit() non-failing v2

dma_fence_wait(old, false) is not interruptible and cannot return an
error. Drop the unreachable error handling in amdgpu_fence_emit().

Since the function can no longer fail, convert amdgpu_fence_emit() to
return void and remove return value handling from all callers.

v2:
- Add comment explaining why dma_fence_wait(..., false)
  return value is ignored (Alex)

Suggested-by: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>