arch/tile: avoid false corrupt frame warning in early boot

With lockstat we can end up trying to get a backtrace before
"high_memory" is initialized, so don't worry about range testing
if it is zero.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/process.c

@@ -286,7 +286,7 @@ struct task_struct *validate_current(void)
 	static struct task_struct corrupt = { .comm = "<corrupt>" };
 	struct task_struct *tsk = current;
 	if (unlikely((unsigned long)tsk < PAGE_OFFSET ||
-		     (void *)tsk > high_memory ||
+		     (high_memory && (void *)tsk > high_memory) ||
 		     ((unsigned long)tsk & (__alignof__(*tsk) - 1)) != 0)) {
 		pr_err("Corrupt 'current' %p (sp %#lx)\n", tsk, stack_pointer);
 		tsk = &corrupt;