cpufreq: ia64: Fix a memory leak in acpi_cpufreq_cpu_exit()

freq_table should be alloced in ->init and freed in ->exit, but it
it is not freed.  Fix this memory leak in acpi_cpufreq_cpu_exit().

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>