ACPI: fix boot with acpi=off

Fix acpi_ac/battery boot with acpi=off

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/ac.c b/drivers/acpi/ac.c
index 96309b9..11abc7b 100644
--- a/drivers/acpi/ac.c
+++ b/drivers/acpi/ac.c
@@ -285,6 +285,8 @@
 {
 	int result;
 
+	if (acpi_disabled)
+		return -ENODEV;
 
 	acpi_ac_dir = acpi_lock_ac_dir();
 	if (!acpi_ac_dir)