x32: Only clear TIF_X32 flag once

Commits bb212724 and d1a797f3

 both added a call to
clear_thread_flag(TIF_X32) under set_personality_64bit() - only one is
needed.

Signed-off-by: Bobby Powers <bobbypowers@gmail.com>
Link: http://lkml.kernel.org/r/1330228774-24223-1-git-send-email-bobbypowers@gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>