Bluetooth: Use hci_connect_sco directly

hci_connect is a super function for connecting hci protocols. But the
voice_setting parameter (introduced in subsequent patches) is only
needed by SCO and security requirements are not needed for SCO channels.
Thus, it makes sense to have a separate function for SCO.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@linux.intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>