staging: comedi: add comedi_write_array_to_buffer()

The "comedi_fc" module contains a few functions useful to Comedi
drivers.  Their functionality is being migrated to the core "comedi"
module and renamed to start with the prefix `comedi_`.  As part of this
migration, move `cfc_write_array_to_buffer()` into the core comedi
module and rename it to `comedi_write_array_to_buffer()`.  Change the
external declaration of `cfc_write_array_to_buffer()` into an inline
function that calls `comedi_write_array_to_buffer()`.

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>