intel_pstate: Use sample.core_avg_perf in get_avg_pstate()

Notice that get_avg_pstate() can use sample.core_avg_perf instead of
carrying the same division again, so make it do that.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 19712e2..ff5c591 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1218,8 +1218,8 @@
 
 static inline int32_t get_avg_pstate(struct cpudata *cpu)
 {
-	return div64_u64(cpu->pstate.max_pstate_physical * cpu->sample.aperf,
-			 cpu->sample.mperf);
+	return mul_ext_fp(cpu->pstate.max_pstate_physical,
+			  cpu->sample.core_avg_perf);
 }
 
 static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)