staging: comedi: ni_660x: remove struct NI_660xRegisterData 'name'

This member of the struct is not used, and just takes up space. Remove it.
Instead, add the enum ni_660x_register indexes to the table to clarify, and
document, the entries.
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>