Fix the following warnings from sparse due to casting to/from an __iomem
annotated variable:

drivers/watchdog/sirfsoc_wdt.c:48:18: warning: incorrect type in assignment (different address spaces)
drivers/watchdog/sirfsoc_wdt.c:48:18:    expected void [noderef] <asn:2>*wdt_base
drivers/watchdog/sirfsoc_wdt.c:48:18:    got void *
drivers/watchdog/sirfsoc_wdt.c:64:18: warning: incorrect type in assignment (different address spaces)
drivers/watchdog/sirfsoc_wdt.c:64:18:    expected void [noderef] <asn:2>*wdt_base
drivers/watchdog/sirfsoc_wdt.c:64:18:    got void *
drivers/watchdog/sirfsoc_wdt.c:82:54: warning: incorrect type in initializer (different address spaces)
drivers/watchdog/sirfsoc_wdt.c:82:54:    expected void [noderef] <asn:2>*wdt_base
drivers/watchdog/sirfsoc_wdt.c:82:54:    got void *
drivers/watchdog/sirfsoc_wdt.c:99:54: warning: incorrect type in initializer (different address spaces)
drivers/watchdog/sirfsoc_wdt.c:99:54:    expected void [noderef] <asn:2>*wdt_base
drivers/watchdog/sirfsoc_wdt.c:99:54:    got void *
drivers/watchdog/sirfsoc_wdt.c:153:44: warning: incorrect type in argument 2 (different address spaces)
drivers/watchdog/sirfsoc_wdt.c:153:44:    expected void *data
drivers/watchdog/sirfsoc_wdt.c:153:44:    got void [noderef] <asn:2>*[assigned] base

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>