staging: comedi: comedidev.h: remove 'new_size' param from subdevice (*buf_change)

This parameter is never used by any of the comedi drivers that provide a
(*buf_change) callback. If the 'new_size' is needed in the callback it can
be found from the 's->async->prealloc_bufsz' as done in the ni_pcidio driver.

Remove the unused parameter.

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>