sunrpc: mark all struct svc_version instances as const

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index dc2a29a..1c0ce9c 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -225,8 +225,8 @@ static inline void nfs_fs_proc_exit(void)
 #endif
 
 /* callback_xdr.c */
-extern struct svc_version nfs4_callback_version1;
-extern struct svc_version nfs4_callback_version4;
+extern const struct svc_version nfs4_callback_version1;
+extern const struct svc_version nfs4_callback_version4;
 
 struct nfs_pageio_descriptor;
 /* pagelist.c */