staging: comedi: jr3_pci: remove 'channel_no' from subdevice private data

This member of the subdevice private data is just the subdevice 'index'. Use
that instead and remove the member.

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>