intel_pstate: Fix type mismatch warning

The expression in line 398 of intel_pstate.c causes the following
warning to be emitted:

drivers/cpufreq/intel_pstate.c:398:3: warning: left shift count >= width of type

which happens because unsigned long is 32-bit on some architectures.

Fix that by using a helper u64 variable and simplify the code
slightly.
Tested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/intel_pstate.c

@@ -383,6 +383,7 @@ static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max)
 static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
 {
 	int max_perf, min_perf;
+	u64 val;
 
 	intel_pstate_get_min_max(cpu, &min_perf, &max_perf);
 
@@ -394,11 +395,11 @@ static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
 	trace_cpu_frequency(pstate * 100000, cpu->cpu);
 
 	cpu->pstate.current_pstate = pstate;
+	val = pstate << 8;
 	if (limits.no_turbo)
-		wrmsrl(MSR_IA32_PERF_CTL, BIT(32) | (pstate << 8));
-	else
-		wrmsrl(MSR_IA32_PERF_CTL, pstate << 8);
+		val |= (u64)1 << 32;
 
+	wrmsrl(MSR_IA32_PERF_CTL, val);
 }
 
 static inline void intel_pstate_pstate_increase(struct cpudata *cpu, int steps)