cpufreq: sh: Remove sh_cpufreq_cpu_ready()

The ->ready() callback is going away and since we don't do any important
stuff in sh_cpufreq_cpu_ready(), remove it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>