regression with sunxi: psci: avoid error address-of-packed-member

[Nuno Gonçalves]

After [1] on a Orange Pi Zero I hang on Starting kernel.

While this commit changed the order of clamp_set fixing it did not
solve the problem for me. It appears that the problem is simply that a
memcpy to sunxi_prcm_reg.cpu_pwroff does not have the same behaviour
as writing a single bit.

Thanks,
Nuno

[1] https://github.com/u-boot/u-boot/commit/9bd34a69a453d409792e08c00953ce8862145e65