watchdog: Staticise nuc900_wdt

It is only used in this driver, so no need to make the symbol global.
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

drivers/watchdog/nuc900_wdt.c

@@ -72,7 +72,7 @@ struct nuc900_wdt {
 };
 
 static unsigned long nuc900wdt_busy;
-struct nuc900_wdt *nuc900_wdt;
+static struct nuc900_wdt *nuc900_wdt;
 
 static inline void nuc900_wdt_keepalive(void)
 {