Implement raw output callback which is used by hidraw to send raw data to
the underlying device.

Without this patch, the userspace hidraw-based applications can't send
output reports to HID Bluetooth devices.
Reported-and-tested-by: Brian Gunn <bgunn@solekai.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>