m68knommu: use TRHEAD_SIZE instead of hard constant

Use THREAD_SIZE instead of a hard constant.
Signed-off-by: NPhilippe De Muyter <phdm@macqel.be>
Signed-off-by: NGreg Ungerer <gerg@uclinux.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/m68knommu/kernel/process.c

@@ -377,7 +377,7 @@ unsigned long get_wchan(struct task_struct *p)
 	fp = ((struct switch_stack *)p->thread.ksp)->a6;
 	do {
 		if (fp < stack_page+sizeof(struct thread_info) ||
-		    fp >= 8184+stack_page)
+		    fp >= THREAD_SIZE-8+stack_page)
 			return 0;
 		pc = ((unsigned long *)fp)[1];
 		if (!in_sched_functions(pc))