staging: comedi: jr3_pci: fix initial range[8] max value

`jr3_pci_alloc_spriv()` initializes `spriv->range[8]` to use a maximum
value of 65536, but that will be overwritten with 65535 at a later time
by `jr3_pci_poll_subdevice()` once the "set full scales" command is
complete.  The initial setting looks like a mistake.  This range is only
associated with a couple of dummy channels (channels 56 and 57) to read
back the model number and serial number, so no user code should be
attempting to convert those numbers to physical units.  Just change the
initial value to 65535 to match the final value.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>