staging: comedi: jr3_pci: rename some local vars in the (*attach)

For aesthetics, rename the subdevice private data pointer from 'p'
to 'spriv' and the variable used to check the errno from 'result'
to 'ret'.

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>