ACPI: throttling: fix build warning

Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/processor_throttling.c

@@ -987,7 +987,7 @@ static int acpi_processor_set_throttling_ptc(struct acpi_processor *pr,
 int acpi_processor_set_throttling(struct acpi_processor *pr, int state)
 {
 	cpumask_t saved_mask;
-	int ret;
+	int ret = 0;
 	unsigned int i;
 	struct acpi_processor *match_pr;
 	struct acpi_processor_throttling *p_throttling;