ACPI: CPPC: clean up acpi_get_psd_map()

In acpi_get_psd_map() variable all_cpu_data[] can't be NULL and variable
match_cpc_ptr has been checked before, no need check again at the end of
the funchtion.

Some additional optimizations can be made on top of that.

Signed-off-by: Liguang Zhang <zhangliguang@linux.alibaba.com>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>