powerpc/macio: Make remove callback of macio driver void returned

Commit fc7a6209 ("bus: Make remove callback return void") forces
bus_type::remove be void-returned, it doesn't make much sense for any
bus based driver implementing remove callbalk to return non-void to
its caller.

This change is for macio bus based drivers.

Signed-off-by: Dawei Li <set_pte_at@outlook.com>
Acked-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/TYCP286MB232391520CB471E7C8D6EA84CAD19@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM