staging: comedi: adl_pci9111: remove pci9111_ai_channel_[gs]et macros

These macros rely on a local variable having a specific name.

The comedi code makes sure the channel number is valid so the mask
of PCI9111_CHANNEL_MASK can be remove.

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>