i2c: efm32: fix binding doc

Fix dt compatible string in the binding document which was changed
during review in the driver, but it seem I messed up to adapt the
documentation accordingly.

Also change status from "disabled" to "ok" which makes more sense for an
example.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>