sfc: allow asynchronous MCDI without completion function

Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/mcdi.c

@@ -548,7 +548,10 @@ static bool efx_mcdi_complete_async(struct efx_mcdi_iface *mcdi, bool timeout)
 		efx_mcdi_display_error(efx, async->cmd, async->inlen, errbuf,
 				       err_len, rc);
 	}
-	async->complete(efx, async->cookie, rc, outbuf, data_len);
+
+	if (async->complete)
+		async->complete(efx, async->cookie, rc, outbuf,
+				min(async->outlen, data_len));
 	kfree(async);
 
 	efx_mcdi_release(mcdi);