f2fs: add help function META_MAPPING

Introduce help function META_MAPPING() to get the cache meta blocks'
address space.

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 5ab3981..117e30f 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -533,6 +533,11 @@
 	return (struct dirty_seglist_info *)(SM_I(sbi)->dirty_info);
 }
 
+static inline struct address_space *META_MAPPING(struct f2fs_sb_info *sbi)
+{
+	return sbi->meta_inode->i_mapping;
+}
+
 static inline void F2FS_SET_SB_DIRT(struct f2fs_sb_info *sbi)
 {
 	sbi->s_dirty = 1;