hw/xfree86: nobus.c shouldn't define a static function

Having this function be static generates a compiler warning.
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

hw/xfree86/os-support/bus/nobus.c

-static void
+void
+__noop_to_appease_ar__(void);
+
+void
 __noop_to_appease_ar__(void)
 {
     return;