asus-wmi: Fix unused function build warning

Fix the following build warning

CC [M]  drivers/platform/x86/asus-wmi.o
drivers/platform/x86/asus-wmi.c:1356:13: warning: ‘do_nothing’ defined but not used [-Wunused-function]

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/asus-wmi.c

@@ -1353,11 +1353,6 @@ static int is_display_toggle(int code)
 	return 0;
 }
 
-static void do_nothing(void)
-{
-	return;
-}
-
 static void asus_wmi_notify(u32 value, void *context)
 {
 	struct asus_wmi *asus = context;