cpufreq: ACPI: Remove freq_table from acpi_cpufreq_data

The freq-table is stored in struct cpufreq_policy also and there is
absolutely no need of keeping a copy of its reference in struct
acpi_cpufreq_data. Drop it.

Also policy->freq_table can't be NULL in the target() callback, remove
the useless check as well.

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