staging: comedi: adl_pci9118: rename PCI9118_SCANMOD define

For aesthetics, rename this define used for the analog input auto scan
mode register.

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