Documentation: i2c: fix references to other documents

Similar to commit fe99b819 ("docs: i2c: i2c-sysfs: fix hyperlinks"),
make other links in documentation consistent with the preferred way.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>