ACPI: processor: thermal: avoid cpufreq_get_policy()

cpu_has_cpufreq() stores a 'struct cpufreq_policy' on the stack.
Unfortunately, with debugging options enabled, the structure can be
larger than 1024 bytes, which causes a compiler warning/error.

(actually observed: 1184 bytes).

Therefore: Switch to cpufreq_cpu_get().

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>