x86, mm, trivial: Remove unnecessary get_order() in free_thread_info()

Because THREAD_SIZE is defined as PAGE_SIZE << THREAD_ORDER on x86, the
call of get_order(THREAD_SIZE) can be replaced with THREAD_ORDER.

Signed-off-by: Zhao Jin <cronozhj@gmail.com>
Link: http://lkml.kernel.org/r/4E4FB5A9.700@gmail.com


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>