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/libbsc/bsc_api.c b/openbsc/src/libbsc/bsc_api.c
index 253326f..4dba3e9 100644
--- a/openbsc/src/libbsc/bsc_api.c
+++ b/openbsc/src/libbsc/bsc_api.c
@@ -406,8 +406,7 @@
 	}
 
 	/* we will now start the timer to complete the assignment */
-	conn->T10.cb = assignment_t10_timeout;
-	conn->T10.data = conn;
+	osmo_timer_setup(&conn->T10, assignment_t10_timeout, conn);
 	osmo_timer_schedule(&conn->T10, GSM0808_T10_VALUE);
 	return 0;