staging: comedi: s626: add comedi "chan" number to struct s626_enc_info

Add the comedi "chan" number to the encoder private data so we can then
remove some of the members of the private data.

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>