shared/gatt-client: Fix discover_secondary_cb()

If included services discovery cannot be started, the services discovery
operation has failed.

(cherry picked from commit 93f8d6ed1ae16283eee4974f74e857b07eddef60)

Change-Id: I9724c2057b2fad68d40bc6a582613080089b8018
diff --git a/src/shared/gatt-client.c b/src/shared/gatt-client.c
index 84145e7..dc98aaa 100644
--- a/src/shared/gatt-client.c
+++ b/src/shared/gatt-client.c
@@ -1027,6 +1027,7 @@
 	util_debug(client->debug_callback, client->debug_data,
 				"Failed to start included services discovery");
 	discovery_op_unref(op);
+	success = false;
 
 done:
 	discovery_op_complete(op, success, att_ecode);