mm/damon/reclaim: use resource_size function on resource object

Fix the following coccicheck warnings:

./mm/damon/reclaim.c:241:30-33: WARNING: Suspicious code. resource_size is maybe missing with res.

Link: https://lkml.kernel.org/r/20220507032512.129598-1-jiapeng.chong@linux.alibaba.comSigned-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: "Boehme, Markus" <markubo@amazon.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/reclaim.c

@@ -238,7 +238,7 @@ static int walk_system_ram(struct resource *res, void *arg)
 {
 	struct damon_reclaim_ram_walk_arg *a = arg;
 
-	if (a->end - a->start < res->end - res->start) {
+	if (a->end - a->start < resource_size(res)) {
 		a->start = res->start;
 		a->end = res->end;
 	}