drm/amdgpu: fix the issue that retry constantly once the buffer is oversize

We cannot modify initial_domain every time while the retry starts. That
will cause the busy waiting that unable to switch to GTT while the vram
is not enough.

Fixes: f8aab604

 ("drm/amdgpu: Initialise drm_gem_object_funcs for imported BOs")

Signed-off-by: Huang Rui <ray.huang@amd.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>
Cc: stable@vger.kernel.org