staging: comedi: comedi_buf: remove comedi_buf_put()

All comedi drivers now use comedi_buf_write_samples() to add the samples to
the async buffer. Remove this unused function.

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>