ACPI: Cleanup sparse warning on acpi_os_initialize1()

This patch cleans up the following sparse warning:

# make C=2 drivers/acpi/osl.o
...
drivers/acpi/osl.c:1775:20: warning: symbol 'acpi_os_initialize1' was not declared. Should it be static?
...
  CC      drivers/acpi/osl.o
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/bus.c

@@ -617,7 +617,6 @@ static int __init acpi_bus_init(void)
 {
 	int result;
 	acpi_status status;
-	extern acpi_status acpi_os_initialize1(void);
 
 	acpi_os_initialize1();
 

drivers/acpi/internal.h

@@ -23,6 +23,7 @@
 
 #define PREFIX "ACPI: "
 
+acpi_status acpi_os_initialize1(void);
 int init_acpi_device_notify(void);
 int acpi_scan_init(void);
 #ifdef	CONFIG_ACPI_PCI_SLOT

drivers/acpi/osl.c

@@ -52,6 +52,7 @@
 #include <acpi/acpi.h>
 #include <acpi/acpi_bus.h>
 #include <acpi/processor.h>
+#include "internal.h"
 
 #define _COMPONENT		ACPI_OS_SERVICES
 ACPI_MODULE_NAME("osl");