Coverity doesn't like that the return value of bdrv_check_update_perm()
stays unused only in this place (CID 1399710).

Even if checking local_err should be equivalent to checking ret < 0,
let's switch to using the return value to be more consistent (and in
case of a bug somewhere down the call chain, forgetting to assign errp
is more likely than returning 0 for an error case).
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>