pinctrl: mcp23s08: Print error message when regmap init fails

It is useful for debugging to have the error message printed
when regmap initialisation fails. Add it to the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Martin Hundebøll <martin@geanix.com>
Link: https://lore.kernel.org/r/20201009180856.4738-2-andriy.shevchenko@linux.intel.com
Tested-by: Jan Kundrát <jan.kundrat@cesnet.cz>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinctrl-mcp23s08_spi.c

@@ -126,6 +126,8 @@ static int mcp23s08_spi_regmap_init(struct mcp23s08 *mcp, struct device *dev,
 	copy->name = name;
 
 	mcp->regmap = devm_regmap_init(dev, &mcp23sxx_spi_regmap, mcp, copy);
+	if (IS_ERR(mcp->regmap))
+		dev_err(dev, "regmap init failed for %s\n", mcp->chip.label);
 	return PTR_ERR_OR_ZERO(mcp->regmap);
 }