Remove deprecated UNUSED macro (5/5)

Include osi.h for UNUSED_ATTR.

Test: mma -j32

Change-Id: I43260669dc1f54639e46cc9620093d727ee86276
diff --git a/bta/sys/bta_sys_conn.cc b/bta/sys/bta_sys_conn.cc
index 6b1cc2c..1098f9c 100644
--- a/bta/sys/bta_sys_conn.cc
+++ b/bta/sys/bta_sys_conn.cc
@@ -27,6 +27,7 @@
 #include "bta_sys.h"
 #include "bta_sys_int.h"
 #include "bt_common.h"
+#include "osi/include/osi.h"
 #include "utl.h"
 
 /*******************************************************************************