mm/zsmalloc.c: rework the list_add code in insert_zspage()

Rework the list_add code to make it more readable and simple.

Link: https://lkml.kernel.org/r/20201015130107.65195-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/zsmalloc.c

@@ -726,13 +726,10 @@ static void insert_zspage(struct size_class *class,
 	 * We want to see more ZS_FULL pages and less almost empty/full.
 	 * Put pages with higher ->inuse first.
 	 */
-	if (head) {
-		if (get_zspage_inuse(zspage) < get_zspage_inuse(head)) {
-			list_add(&zspage->list, &head->list);
-			return;
-		}
-	}
-	list_add(&zspage->list, &class->fullness_list[fullness]);
+	if (head && get_zspage_inuse(zspage) < get_zspage_inuse(head))
+		list_add(&zspage->list, &head->list);
+	else
+		list_add(&zspage->list, &class->fullness_list[fullness]);
 }
 
 /*