DRIVER_MODULE(9): Correct the SYNOPSIS of EARLY_DRIVER_MODULE()

The man page SYNOPSIS for EARLY_DRIVER_MODULE() shows that it has
an "enum sysinit_elem_order order" argument.

The actual macro in sys/bus.h does not have an order argument.

PR: 256103
Reported by: J.R. Oldroyd <fbsd at opal dot com>
Reviewed by: markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D30411