staging: comedi: s626: prefix macros in s626.c

Prefix the macros defined in "s626.c" with `S626_`.  Macro `VECT0` is
unused, so remove it.

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>