f2fs: introduce help function F2FS_NODE()

Introduce help function F2FS_NODE() to simplify the conversion of node_page to
f2fs_node.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 0a352b6..2dfd584 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -455,6 +455,11 @@
 	return (struct f2fs_checkpoint *)(sbi->ckpt);
 }
 
+static inline struct f2fs_node *F2FS_NODE(struct page *page)
+{
+	return (struct f2fs_node *)page_address(page);
+}
+
 static inline struct f2fs_nm_info *NM_I(struct f2fs_sb_info *sbi)
 {
 	return (struct f2fs_nm_info *)(sbi->nm_info);
@@ -813,7 +818,7 @@
 
 static inline bool IS_INODE(struct page *page)
 {
-	struct f2fs_node *p = (struct f2fs_node *)page_address(page);
+	struct f2fs_node *p = F2FS_NODE(page);
 	return RAW_IS_INODE(p);
 }
 
@@ -827,7 +832,7 @@
 {
 	struct f2fs_node *raw_node;
 	__le32 *addr_array;
-	raw_node = (struct f2fs_node *)page_address(node_page);
+	raw_node = F2FS_NODE(node_page);
 	addr_array = blkaddr_in_node(raw_node);
 	return le32_to_cpu(addr_array[offset]);
 }