kcore: fix test for end of list

"m" is never NULL here.  We need a different test for the end of list
condition.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/kcore.c

@@ -490,7 +490,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		}
 		read_unlock(&kclist_lock);
 
-		if (m == NULL) {
+		if (&m->list == &kclist_head) {
 			if (clear_user(buffer, tsz))
 				return -EFAULT;
 		} else if (is_vmalloc_or_module_addr((void *)start)) {