Bluetooth: Return ENODATA in hci_req_run

In case the HCI request queue is empty, hci_req_run should return
ENODATA instead of EINVAL. This way, hci_req_run returns a more
meaningful error value.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Acked-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>