cpufreq: intel_pstate: Fold intel_pstate_max_within_limits() into caller

Fold intel_pstate_max_within_limits() into its only caller.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>