Samples: Bluetooth: Fix unicast client ASCS discovery

The unicast client used the BT_DATA_UUID16_SOME and
BT_DATA_UUID16_ALL instead BT_DATA_SVC_DATA16 for
discovering ASCS servers.

BT_DATA_SVC_DATA16 is the right one to use, as that
is mandatory for a server to advertise, and the UUID
ones are only recommended. Furthermore, the service data
of the ASCS server can now also be retrieved.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>