watchdog: ie6xx_wdt needs io.h

Fix build error by including <linux/io.h>:

drivers/watchdog/ie6xx_wdt.c:97:2: error: implicit declaration of function 'outb'
drivers/watchdog/ie6xx_wdt.c:133:2: error: implicit declaration of function 'outl'
drivers/watchdog/ie6xx_wdt.c:161:2: error: implicit declaration of function 'inb'
drivers/watchdog/ie6xx_wdt.c:199:3: error: implicit declaration of function 'inl'
drivers/watchdog/ie6xx_wdt.c:203:3: error: implicit declaration of function 'inw'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>