fpga: altera-ps-spi: Fix getting of optional confd gpio

Currently the driver does not handle EPROBE_DEFER for the confd gpio.
Use devm_gpiod_get_optional() instead of devm_gpiod_get() and return
error codes from altera_ps_probe().

Fixes: 5692fae0 ("fpga manager: Add altera-ps-spi driver for Altera FPGAs")
Signed-off-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/altera-ps-spi.c

@@ -210,7 +210,7 @@ static int altera_ps_write_complete(struct fpga_manager *mgr,
 		return -EIO;
 	}
 
-	if (!IS_ERR(conf->confd)) {
+	if (conf->confd) {
 		if (!gpiod_get_raw_value_cansleep(conf->confd)) {
 			dev_err(&mgr->dev, "CONF_DONE is inactive!\n");
 			return -EIO;
@@ -289,10 +289,13 @@ static int altera_ps_probe(struct spi_device *spi)
 		return PTR_ERR(conf->status);
 	}
 
-	conf->confd = devm_gpiod_get(&spi->dev, "confd", GPIOD_IN);
+	conf->confd = devm_gpiod_get_optional(&spi->dev, "confd", GPIOD_IN);
 	if (IS_ERR(conf->confd)) {
-		dev_warn(&spi->dev, "Not using confd gpio: %ld\n",
-			 PTR_ERR(conf->confd));
+		dev_err(&spi->dev, "Failed to get confd gpio: %ld\n",
+			PTR_ERR(conf->confd));
+		return PTR_ERR(conf->confd);
+	} else if (!conf->confd) {
+		dev_warn(&spi->dev, "Not using confd gpio");
 	}
 
 	/* Register manager with unique name */