For recursive renaming, simplify the code by moving `zhrp` and
`parentname` to inner scope. `zhrp` is only used to test existence
of a parent dataset for recursive dataset dir scan since ba6a24026c.
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Giuseppe Di Natale <guss80@gmail.com>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@osnexus.com>
Closes#8815
e4a11acfac