i2c: mux: pca954x: retry updating the mux selection on failure

commit 463e8f84 upstream.

The cached value of the last selected channel prevents retries on the
next call, even on failure to update the selected channel. Fix that.
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/i2c/muxes/i2c-mux-pca954x.c

@@ -161,7 +161,7 @@ static int pca954x_select_chan(struct i2c_adapter *adap,
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(adap, client, regval);
-		data->last_chan = regval;
+		data->last_chan = ret ? 0 : regval;
 	}
 
 	return ret;