staging: comedi: s626: remove my_cr[ab] from encoder private data

These members of the encoder private data can be calculated based on
the comedi channel stored in the 'chan' member of the private data.
Do that instead and remove the unnecessary members.
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>