Since we need to read voltages of parents as part of setting supply
voltages we need to be able to do get_voltage() internally without
taking locks so reorganize the locking to take locks on the full tree on
entry rather than as we recurse when called externally.
Reported-by: NJohn Stultz <john.stultz@linaro.org>
Tested-by: NJohn Stultz <john.stultz@linaro.org>
Signed-off-by: NMark Brown <broonie@kernel.org>