cpufreq: acpi-cpufreq: Mark 'dummy' variable as __always_unused

If we fail to use a variable, even a 'dummy' one, then the compiler
complains that it is set but not used.  We know this is fine, so we
set it as __always_unused to let the compiler know.

Fixes the following W=1 kernel build warning(s):

 drivers/cpufreq/acpi-cpufreq.c: In function ‘cpu_freq_read_intel’:
 drivers/cpufreq/acpi-cpufreq.c:247:11: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]
 drivers/cpufreq/acpi-cpufreq.c: In function ‘cpu_freq_read_amd’:
 drivers/cpufreq/acpi-cpufreq.c:265:11: warning: variable ‘dummy’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Lee Jones <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: Lee Jones

drivers/cpufreq/acpi-cpufreq.c

@@ -244,7 +244,7 @@ static unsigned extract_freq(struct cpufreq_policy *policy, u32 val)
 
 static u32 cpu_freq_read_intel(struct acpi_pct_register *not_used)
 {
-	u32 val, dummy;
+	u32 val, dummy __always_unused;
 
 	rdmsr(MSR_IA32_PERF_CTL, val, dummy);
 	return val;
@@ -261,7 +261,7 @@ static void cpu_freq_write_intel(struct acpi_pct_register *not_used, u32 val)
 
 static u32 cpu_freq_read_amd(struct acpi_pct_register *not_used)
 {
-	u32 val, dummy;
+	u32 val, dummy __always_unused;
 
 	rdmsr(MSR_AMD_PERF_CTL, val, dummy);
 	return val;