staging: comedi: comedi_fc.h: use comedi_write_array_to_buffer()

Since `cfc_write_array_to_buffer()` is just an inline function that
calls `comedi_write_array_to_buffer()`, replace calls to the former to
the latter in the "comedi_fc.h" header.  This is part of the migration
of functionality from the "comedi_fc" module to the core "comedi"
module.

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>