spi: lm70llp: fix links in doc and comments

Update links in the documentation and in-code comments which point to
the datasheet and schematic.

The current links don't work because National Semiconductor (which is
the manufacturer of this board and lm70) has been a part of Texas
Instruments since 2011 and hence http://www.national.com/ doesn't work
anymore.

Fixes: 78961a57 ("spi_lm70llp parport adapter driver")
Fixes: 2b730051

 ("hwmon: (lm70) Code streamlining and cleanup")
Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com>
Link: https://msgid.link/r/20240318154540.90613-2-five231003@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>