pinctrl: mcp23s08: spi: Fix regmap allocation for mcp23s18

Fixes issue created by 9b3e4207.

It wasn't possible for one_regmap_config to be non-NULL at the point
it was tested for mcp23s18 devices.

Applied the same pattern of allocating one_regmap_config using
devm_kmemdump() and then initializing the local regmap structure
from that.
Signed-off-by: Jason Kridner <jdk@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinctrl-mcp23s08.c

@@ -832,8 +832,13 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 		break;
 
 	case MCP_TYPE_S18:
+		one_regmap_config =
+			devm_kmemdup(dev, &mcp23x17_regmap,
+				sizeof(struct regmap_config), GFP_KERNEL);
+		if (!one_regmap_config)
+			return -ENOMEM;
 		mcp->regmap = devm_regmap_init(dev, &mcp23sxx_spi_regmap, mcp,
-					       &mcp23x17_regmap);
+					       one_regmap_config);
 		mcp->reg_shift = 1;
 		mcp->chip.ngpio = 16;
 		mcp->chip.label = "mcp23s18";