mfd: rk808: Permit having multiple PMIC instances

This set each cells id to PLATFORM_DEVID_NONE to allow multiple
instances of each cell in case multiple PMICs handled by the rk808
driver are probed.

This fixes probing a RK818 and a RK817 on the Odroid Go Ultra
devices.

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221025-rk808-multi-v2-0-d292d51ada81@linaro.org