This patch fixes following compiler warning when build via make W=1:

drivers/acpi/battery.c:149:52: warning: no previous prototype for ‘acpi_battery_present’ [-Wmissing-prototypes]
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>