Drivers: hv: util: Properly pack the data for file copy functionality

Properly pack the data for file copy functionality. Patch based on
investigation done by Matej Muzila <mmuzila@redhat.com>

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reported-by:  <qge@redhat.com>
Cc: <stable@vger.kernel.org>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>