watchdog: wdt_pci: fix build error if define SOFTWARE_REBOOT

To fix following build error when SOFTWARE_REBOOT is defined:

  CC [M]  driver/watchdog/wdt_pci.o
driver/watchdog/wdt_pci.c: In function 'wdtpci_interrupt':
driver/watchdog/wdt_pci.c:335:3: error: too many arguments to function 'emergency_restart'
   emergency_restart(NULL);
   ^
In file included from driver/watchdog/wdt_pci.c:51:0:
include/linux/reboot.h:80:13: note: declared here
 extern void emergency_restart(void);
             ^

Signed-off-by: Shile Zhang <shile.zhang@nokia.com>
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>