staging: comedi: jr3_pci: tidy up jr3_pci_poll_subdevice()

Refactor the function to reduce the indent level.

For aesthetics, rename the subdevice private data pointer from 'p'
to 'spriv'.

Rename the lacal variable used for the channel->full_scale to 'fs'
to reduce the line lengths.

Remove the setting of range[8]. The min,max values are the same as
the ones used when the subdevice private data was allocated and
initialized.

Remove the poll_delay_min_max() that are the same as the default.

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>