staging: comedi: s626: rename CamelCase in struct enc_private

Rename the CamelCase members of `struct enc_private`.  Since most of
those are function pointers pointing to functions with similar names as
the members, rename the functions they point to as well.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>