Fix GATT Characteristic discovery (server side)

The pointer was not properly incremented, which resulted in trashes
being sent during GATT discovery.

This issue was introduced in commit
2238a88f (Use one type for UUID)

Bug: 66912853
Test: sl4a GATT read test
Change-Id: Ib57ad050ff17852f9b2fec9c51cad246235e3e80