hw/ppc/prep: Remove superfluous call to soundhw_init()

When using the 40p machine, soundhw_init() is currently called twice,
one time from vl.c and one time from ibm_40p_init(). The call in
ibm_40p_init() was likely just a copy-and-paste from a old version
of the prep machine - but there the call to audio_init() (which was
the previous name of this function) has been removed many years ago
already, with commit b3e6d591
("audio: enable PCI audio cards for all PCI-enabled targets"), so
we certainly also do not need the soundhw_init() in the 40p function
anymore nowadays.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Sahid Ferdjaoui <sferdjao@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>