mt8173: fixed booting issue

Signed-off-by: SY Chiu <sy.chiu@linaro.org>
Tested-by: SY Chiu <sy.chiu@linaro.org> (MT8173 EVB)
Tested-by: Joakim Bech <joakim.bech@linaro.org> (MT8173 EVB)
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>