staging: comedi: jr3_pci: use comedi_alloc_spriv()

Use the helper function to allocate the subdevice private data. This
sets the s->private variable for us and allows the comedi core to
automatically kfree() the memory during the (*detach).

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>