Bluetooth: ISO: Allow binding a bcast listener to 0 bises

This makes it possible to bind a broadcast listener to a broadcaster
address without asking for any BIS indexes to sync with.

Signed-off-by: Iulia Tanasescu <iulia.tanasescu@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>