spi: Return error from of_spi_register_master on bad "cs-gpios" property

This makes sure that an error is returned on an incorrectly formed
"cs-gpios" property, but reports success when the "cs-gpios" property is
well formed or missing.

When holes in the cs-gpios property phandle list is used to indicate
that some other form of chipselect is to be used it is important that
failure to read a broken "cs-gpios" property does not silently fail
leading to the spi controller to use an unintended chipselect.
Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi.c

@@ -1067,8 +1067,11 @@ static int of_spi_register_master(struct spi_master *master)
 	nb = of_gpio_named_count(np, "cs-gpios");
 	master->num_chipselect = max(nb, (int)master->num_chipselect);
 
-	if (nb < 1)
+	/* Return error only for an incorrectly formed cs-gpios property */
+	if (nb == 0 || nb == -ENOENT)
 		return 0;
+	else if (nb < 0)
+		return nb;
 
 	cs = devm_kzalloc(&master->dev,
 			  sizeof(int) * master->num_chipselect,