When DM_REGULATOR=n is used the device_get_supply_regulator() function always return -ENOSYS. Change to treat missing support for regulators as a missing optional vdd/vss-supply regulator to reduce error messages being logged. Signed-off-by: Jonas Karlman <jonas@kwiboo.se> Reviewed-by: Kever Yang <kever.yang@rock-chips.com>