cpufreq: dt: Tolerance applies on both sides of target voltage

Tolerance applies on both sides of the target voltage, i.e. both min and
max sides. But while checking if a voltage is supported by the regulator
or not, we haven't taken care of tolerance on the lower side. Fix that.

Cc: Lucas Stach <l.stach@pengutronix.de>
Fixes: 045ee45c

 ("cpufreq: cpufreq-dt: disable unsupported OPPs")
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>