[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>
authored by Dave Jiang and committed by Paul Mackerras 40ebbcbf 3d372548