bus: mvebu-mbus: potential forever loop in mvebu_mbus_init()

"of_id->compatible" is an array and not a pointer so it can never be
NULL.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>