watchdog: ixp4xx_wdt: Fix address space warning

sparse reports the following address space warning.

drivers/watchdog/ixp4xx_wdt.c:122:20: sparse:
	incorrect type in assignment (different address spaces)
drivers/watchdog/ixp4xx_wdt.c:122:20: sparse:
	expected void [noderef] __iomem *base
drivers/watchdog/ixp4xx_wdt.c:122:20: sparse:
	got void *platform_data

Add a typecast to solve the problem.

Fixes: 21a0a29d16 ("watchdog: ixp4xx: Rewrite driver to use core")
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210911042925.556889-1-linux@roeck-us.net
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/ixp4xx_wdt.c

@@ -119,7 +119,7 @@ static int ixp4xx_wdt_probe(struct platform_device *pdev)
 	iwdt = devm_kzalloc(dev, sizeof(*iwdt), GFP_KERNEL);
 	if (!iwdt)
 		return -ENOMEM;
-	iwdt->base = dev->platform_data;
+	iwdt->base = (void __iomem *)dev->platform_data;
 
 	/*
 	 * Retrieve rate from a fixed clock from the device tree if