Bluetooth: hci_conn: Fix not allowing valid CIS ID

Only the number of CIS shall be limited to 0x1f, the CIS ID in the
other hand is up to 0xef.

Fixes: 26afbd82

 ("Bluetooth: Add initial implementation of CIS connections")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>