cpufreq: s3cx4xx: call cpufreq_frequency_table_get_attr()

This exposes frequency table of driver to cpufreq core and is required for core
to guess what the index for a target frequency is, when it calls
cpufreq_frequency_table_target(). And so this driver needs to expose it.

Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>