cpufreq: dt: No need to fetch voltage-tolerance

Its already done by core and we don't need to get it anymore.  And so,
we don't need to get of node in cpufreq_init() anymore, move that to
find_supply_name() instead.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
(cherry picked from commit df2c8ec28e73d47392b8cb24828c15c54819da41)
Signed-off-by: Alex Shi <alex.shi@linaro.org>