staging: comedi: s626: remove struct s626_enc_info

The only member left in this struct is the 'chan' which is the
comedi channel of the encoder.

Remove the struct and refactor the code to pass/use the comedi
channel instead.
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>