[POWERPC] Fix comment in booke_wdt

The early kernel parameter is wdt and not wdt_enable. according to
arch/powerpc/kernel/setup_32.c.
Signed-off-by: Dave Jiang <djiang@mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

drivers/char/watchdog/booke_wdt.c

@@ -24,7 +24,7 @@
 #include <asm/uaccess.h>
 #include <asm/system.h>
 
-/* If the kernel parameter wdt_enable=1, the watchdog will be enabled at boot.
+/* If the kernel parameter wdt=1, the watchdog will be enabled at boot.
  * Also, the wdt_period sets the watchdog timer period timeout.
  * For E500 cpus the wdt_period sets which bit changing from 0->1 will
  * trigger a watchog timeout. This watchdog timeout will occur 3 times, the