In error cases regulator_get_voltage() returns a negative value.
So take care of it.
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>