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>

arch/x86/kernel/process.c

@@ -49,7 +49,7 @@ void free_thread_xstate(struct task_struct *tsk)
 void free_thread_info(struct thread_info *ti)
 {
 	free_thread_xstate(ti->task);
-	free_pages((unsigned long)ti, get_order(THREAD_SIZE));
+	free_pages((unsigned long)ti, THREAD_ORDER);
 }
 
 void arch_task_cache_init(void)