i2c: mux: demux-pinctrl: invalidate properly when switching fails

Make sure the index to the active channel is invalidated when switching
fails.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/muxes/i2c-demux-pinctrl.c

@@ -107,6 +107,7 @@ static int i2c_demux_activate_master(struct i2c_demux_pinctrl_priv *priv, u32 ne
 	of_changeset_revert(&priv->chan[new_chan].chgset);
  err:
 	dev_err(priv->dev, "failed to setup demux-adapter %d (%d)\n", new_chan, ret);
+	priv->cur_chan = -EINVAL;
 	return ret;
 }