staging: comedi: addi_apci_16xx: add missing copyright comment

Add the missing copyright information. This information was
originally in the hwdrv_apci16xx.c file.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>