lua: wrap thread_set_priority with #ifdef HAVE_PRIORITY_SCHEDULING

Should fix a compile-time error on simulator.

Change-Id: I5962479579350ebffe6dcce4f65a629b108ff936
diff --git a/apps/plugins/lua/rocklib.c b/apps/plugins/lua/rocklib.c
index c266516..1e3bc20 100644
--- a/apps/plugins/lua/rocklib.c
+++ b/apps/plugins/lua/rocklib.c
@@ -77,6 +77,7 @@
 }
 #endif
 
+#ifdef HAVE_PRIORITY_SCHEDULING
 RB_WRAP(thread_set_priority)
 {
     unsigned int thread_id = rb->thread_self();
@@ -85,6 +86,7 @@
     lua_pushinteger(L, result);
     return 1;
 }
+#endif
 
 RB_WRAP(current_path)
 {
@@ -778,7 +780,10 @@
 #ifdef HAVE_SCHEDULER_BOOSTCTRL
     RB_FUNC(schedule_cpu_boost),
 #endif
+
+#ifdef HAVE_PRIORITY_SCHEDULING
     RB_FUNC(thread_set_priority),
+#endif
 
     RB_FUNC(current_path),