spi: Warn when a driver's remove callback returns an error

The driver core ignores the return value of struct device_driver::remove
(because in general there is nothing that can be done about that). So
add a warning when an spi driver returns an error.

This simplifies the quest to make struct device_driver::remove return void.
A consequent change would be to make struct spi_driver::remove return void,
but I'm keeping this quest for later (or someone else).
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20201119161604.2633521-3-u.kleine-koenig@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -408,13 +408,20 @@ static int spi_probe(struct device *dev)
 static int spi_remove(struct device *dev)
 {
 	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
-	int ret = 0;
 
-	if (sdrv->remove)
+	if (sdrv->remove) {
+		int ret;
+
 		ret = sdrv->remove(to_spi_device(dev));
+		if (ret)
+			dev_warn(dev,
+				 "Failed to unbind driver (%pe), ignoring\n",
+				 ERR_PTR(ret));
+	}
+
 	dev_pm_domain_detach(dev, true);
 
-	return ret;
+	return 0;
 }
 
 static void spi_shutdown(struct device *dev)