spapr_drc.c: use spapr_drc_release() in isolate_physical/set_unusable

spapr_drc.c: use spapr_drc_release() in isolate_physical/set_unusable

When moving a physical DRC to "Available", drc_isolate_physical() will
move the DRC state to STATE_PHYSICAL_POWERON and, if the DRC is marked
for unplug, call spapr_drc_detach(). For physical DRCs,
drck->empty_state is STATE_PHYSICAL_POWERON, meaning that we're sure
that spapr_drc_detach() will end up calling spapr_drc_release() in the
end.

Likewise, for logical DRCs, drc_set_unusable will move the DRC to
"Unusable" state, setting drc->state to STATE_LOGICAL_UNUSABLE, which is
the drck->empty_state for logical DRCs. spapr_drc_detach() will call
spapr_drc_release() in this case as well.

In both scenarios, spapr_drc_detach() is being used as a
spapr_drc_release(), wrapper, where we also set unplug_requested (which
is already true, otherwise spapr_drc_detach() wouldn't be called in the
first place) and check if drc->state == drck->empty_state, which we also
know it's guaranteed to be true because we just set it.

Just use spapr_drc_release() in these functions to be clear of our
intentions in both these functions.

Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20210222194531.62717-2-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>