gpio: mcp23s08: fix up compilation error

The driver depends on the chip.of_node being present to compile,
which is the case on some target platforms but not others.
Instead, rely on chip.dev->of_node to be used, as struct device
always has an of_node in place.

Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mcp23s08.c

@@ -655,7 +655,8 @@ static int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 
 	mcp->irq_controller = pdata->irq_controller;
 	if (mcp->irq && mcp->irq_controller) {
-		mcp->irq_active_high = of_property_read_bool(mcp->chip.of_node,
+		mcp->irq_active_high =
+			of_property_read_bool(mcp->chip.dev->of_node,
 					      "microchip,irq-active-high");
 
 		if (type == MCP_TYPE_017)