iio: multiplexer: Switch to use dev_err_probe() helper

In the probe path, dev_err() can be replaced with dev_err_probe()
which will check if error code is -EPROBE_DEFER and prints the
error name. It also sets the defer probe reason which can be
checked later through debugfs. It's more simple in error path.

Signed-off-by: Yang Yingliang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/multiplexer/iio-mux.c

···
 	}
 
 	mux->control = devm_mux_control_get(dev, NULL);
-	if (IS_ERR(mux->control)) {
-		if (PTR_ERR(mux->control) != -EPROBE_DEFER)
-			dev_err(dev, "failed to get control-mux\n");
-		return PTR_ERR(mux->control);
-	}
+	if (IS_ERR(mux->control))
+		return dev_err_probe(dev, PTR_ERR(mux->control),
+				     "failed to get control-mux\n");
 
 	i = 0;
 	for (state = 0; state < all_children; state++) {