ACPI: add 'const' to several ACPI file_operations

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/event.c b/drivers/acpi/event.c
index a901b23..959a893 100644
--- a/drivers/acpi/event.c
+++ b/drivers/acpi/event.c
@@ -99,7 +99,7 @@
 	return 0;
 }
 
-static struct file_operations acpi_system_event_ops = {
+static const struct file_operations acpi_system_event_ops = {
 	.open = acpi_system_open_event,
 	.read = acpi_system_read_event,
 	.release = acpi_system_close_event,