drm/amdgpu: remove extra placement for AMDGPU_GEM_CREATE_NO_CPU_ACCESS

This only has the effect of scanning the invisible range twice
since the topdown flag is given anyway.

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