MAINTAINERS: Fix drivers/i2c/busses/i2c-stub.c

This file was moved to drivers/i2c/i2c-stub.c by commit 31d178bf
(i2c-stub: Move to drivers/i2c).

Cc: "Mark M. Hoffman" <mhoffman@lightlink.com>
Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>