iommu: arm-smmu: Ensure add_device is called properly

The add_device callback may be called during arm_smmu_device_dt_probe.
In this case driver_find_device() skips  the device which is
currently being probed. Restore the old list to fix this.

Change-Id: I3ec70fd0f8d4a5eea9e2a8f8a8b91a435a79585f
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>