Bluetooth: Fix unnecessary error message for HCI request completion

In case a command which completes in Command Status was sent using the
hci_cmd_send-family of APIs there would be a misleading error in the
hci_get_cmd_complete function, since the code would be trying to fetch
the Command Complete parameters when there are none.

Avoid the misleading error and silently bail out from the function in
case the received event is a command status.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>