FreeBSD: Do not copy vp into f_data for DTYPE_VNODE files

https://reviews.freebsd.org/D26346

Do not copy vp into f_data for DTYPE_VNODE files. The vnode pointer is
already stored in f_vnode. Use that so f_data can be reused.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10929