staging: comedi: comedi_buf: don't export comedi_write_array_to_buffer()

All the comedi drivers have been converted to use comedi_buf_write_samples().
This function is now only used internally by comedi_buf. Remvoe the export.

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>