f2fs: fix to return correct error number in f2fs_write_begin

Fix the wrong error number in error path of f2fs_write_begin.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -960,8 +960,10 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 
 	/* check inline_data */
 	ipage = get_node_page(sbi, inode->i_ino);
-	if (IS_ERR(ipage))
+	if (IS_ERR(ipage)) {
+		err = PTR_ERR(ipage);
 		goto unlock_fail;
+	}
 
 	set_new_dnode(&dn, inode, ipage, ipage, 0);