cpufreq: intel_pstate: Fix cpu->pstate.turbo_freq initialization

Fix a problem in active mode that cpu->pstate.turbo_freq is initialized
only if HWP-to-frequency scaling factor is refined.

In passive mode, this problem is not exposed, because
cpu->pstate.turbo_freq is set again, later in
intel_cpufreq_cpu_init()->intel_pstate_get_hwp_cap().

Fixes: eb3693f0 ("cpufreq: intel_pstate: hybrid: CPU-specific scaling factor")
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>