shared/gatt-client: Fix secondary service discovery

If the error returned is either BT_ATT_ERROR_ATTRIBUTE_NOT_FOUND or
BT_ATT_ERROR_UNSUPPORTED_GROUP_TYPE the discovery shall be marked as
successful and no error shall be printed.
diff --git a/src/shared/gatt-client.c b/src/shared/gatt-client.c
index d61668d..c369ccb 100644
--- a/src/shared/gatt-client.c
+++ b/src/shared/gatt-client.c
@@ -933,14 +933,16 @@
 	discovery_req_clear(client);
 
 	if (!success) {
-		util_debug(client->debug_callback, client->debug_data,
-					"Secondary service discovery failed."
-					" ATT ECODE: 0x%02x", att_ecode);
 		switch (att_ecode) {
 		case BT_ATT_ERROR_ATTRIBUTE_NOT_FOUND:
 		case BT_ATT_ERROR_UNSUPPORTED_GROUP_TYPE:
+			success = true;
+			att_ecode = 0;
 			goto next;
 		default:
+			util_debug(client->debug_callback, client->debug_data,
+					"Secondary service discovery failed."
+					" ATT ECODE: 0x%02x", att_ecode);
 			goto done;
 		}
 	}