src: use osmo_timer_setup()

Use new function available in libosmocore to set up timers. Compile
tested only.

Change-Id: Ibcfd915688e97d370a888888a83a7c95cbe16819
diff --git a/openbsc/src/gprs/gprs_sgsn.c b/openbsc/src/gprs/gprs_sgsn.c
index 5d9af78..071dd97 100644
--- a/openbsc/src/gprs/gprs_sgsn.c
+++ b/openbsc/src/gprs/gprs_sgsn.c
@@ -889,9 +889,7 @@
 
 void sgsn_inst_init()
 {
-	sgsn->llme_timer.cb = sgsn_llme_check_cb;
-	sgsn->llme_timer.data = NULL;
-
+	osmo_timer_setup(&sgsn->llme_timer, sgsn_llme_check_cb, NULL);
 	osmo_timer_schedule(&sgsn->llme_timer, GPRS_LLME_CHECK_TICK, 0);
 }