bus: sunxi-rsb: Remove the shutdown callback

bus: sunxi-rsb: Remove the shutdown callback

Shutting down the RSB controller prevents communicating with a PMIC
inside pm_power_off(), since that gets called after device_shutdown(),
so it breaks system poweroff on some boards.

Reported-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Tested-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Fixes: 843107498f91 ("bus: sunxi-rsb: Implement suspend/resume/shutdown callbacks")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20221114015749.28490-2-samuel@sholland.org
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>