cpufreq: spear: Use of_property_for_each_u32() instead of open coding

Use of_property_count_u32_elems() and of_property_for_each_u32() instead
of of_find_property() and open coding the property parsing.

This is part of a larger effort to remove callers of of_find_property()
and similar functions. of_find_property() leaks the DT struct property
and data pointers which is a problem for dynamically allocated nodes
which may be freed.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
[Viresh: Fixed build failure and initialize / increment 'i']
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>