ovl: fix incorrect extent info in metacopy case

mainline inclusion
from mainline-v5.11-rc1
commit c11faf32
category: bugfix
bugzilla: NA
CVE: NA

-------------------------------------------------

In metacopy case, we should use ovl_inode_realdata() instead of
ovl_inode_real() to get real inode which has data, so that
we can get correct information of extentes in ->fiemap operation.
Signed-off-by: NChengguang Xu <cgxu519@mykernel.net>
Reviewed-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: NZheng Liang <zhengliang6@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/overlayfs/inode.c

@@ -458,7 +458,7 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		      u64 start, u64 len)
 {
 	int err;
-	struct inode *realinode = ovl_inode_real(inode);
+	struct inode *realinode = ovl_inode_realdata(inode);
 	const struct cred *old_cred;
 
 	if (!realinode->i_op->fiemap)