staging: comedi: serial2002: add some whitespace to the subdevice init

To improve the readability, add some whitespace to the subdevice
init.

Also, for aesthetic reasons and the help with greps, rename the
(*insn_{read,write}) functions.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>