NFSv4: Don't invalidate inode attributes on delegation return

There is no need to declare attributes such as the ctime, mtime and
block size invalid when we're just returning a delegation, so it is
inappropriate to call nfs_post_op_update_inode_force_wcc().
Instead, just call nfs_refresh_inode() after faking up the change
attribute. We know that the GETATTR op occurs before the DELEGRETURN, so
we are safe when doing this.

Fixes: 0bc2c9b4 ("NFSv4: Don't discard the attributes returned by asynchronous DELEGRETURN")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>