Fix unused param warning

libsuspend had only a single warning in the clang build. Fixing it to
make the build clean.

Change-Id: Iaac5f9144b6e6cb122141c6416056c1b2c9aa98e
Author: Edwin Vane <edwin.vane@intel.com>
Reviewed-by: Kevin P Schoedel <kevin.p.schoedel@intel.com>

libsuspend/autosuspend_wakeup_count.c

@@ -38,7 +38,7 @@ static pthread_t suspend_thread;
 static sem_t suspend_lockout;
 static const char *sleep_state = "mem";
 
-static void *suspend_thread_func(void *arg)
+static void *suspend_thread_func(void *arg __attribute__((unused)))
 {
     char buf[80];
     char wakeup_count[20];