driver core: auxiliary bus: Fix typo in the docs

My editor's spell checker noticed that one while I read through the
document.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20210525100042.951717-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>