cpufreq: s5pv210-cpufreq: fix wrong do_div() usage

It is wrong to use do_div() with 32-bit dividends (unsigned long is
32 bits on 32-bit architectures).

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>