ppc: Add a return value to ppc_set_compat() and ppc_set_compat_all()

ppc: Add a return value to ppc_set_compat() and ppc_set_compat_all()

As recommended in "qapi/error.h", indicate success / failure with a
return value. Since ppc_set_compat() is called from a VMState handler,
let's make it an int so that it propagates any negative errno returned
by kvmppc_set_compat(). Do the same for ppc_set_compat_all() for
consistency, even if it isn't called in a context where a negative errno
is required on failure.

This will allow to simplify error handling in the callers.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <20200914123505.612812-3-groug@kaod.org>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>