erofs: directly use wrapper erofs_page_is_managed() when shrinking

We already have the wrapper function to identify managed page.

Link: https://lore.kernel.org/r/20210810065450.1320-1-zbestahu@gmail.com
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/zdata.c

@@ -309,7 +309,6 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
 {
 	struct z_erofs_pcluster *const pcl =
 		container_of(grp, struct z_erofs_pcluster, obj);
-	struct address_space *const mapping = MNGD_MAPPING(sbi);
 	int i;
 
 	/*
@@ -326,7 +325,7 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info *sbi,
 		if (!trylock_page(page))
 			return -EBUSY;
 
-		if (page->mapping != mapping)
+		if (!erofs_page_is_managed(sbi, page))
 			continue;
 
 		/* barrier is implied in the following 'unlock_page' */