Refactor parent dataset handling in libzfs zfs_rename()

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 ba6a240.

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 openzfs#8815

lib/libzfs/libzfs_dataset.c

@@ -4470,8 +4470,6 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 	zfs_cmd_t zc = {"\0"};
 	char *delim;
 	prop_changelist_t *cl = NULL;
-	zfs_handle_t *zhrp = NULL;
-	char *parentname = NULL;
 	char parent[ZFS_MAX_DATASET_NAME_LEN];
 	libzfs_handle_t *hdl = zhp->zfs_hdl;
 	char errbuf[1024];
@@ -4566,18 +4564,21 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 	}
 
 	if (recursive) {
-		parentname = zfs_strdup(zhp->zfs_hdl, zhp->zfs_name);
+		zfs_handle_t *zhrp;
+		char *parentname = zfs_strdup(zhp->zfs_hdl, zhp->zfs_name);
 		if (parentname == NULL) {
 			ret = -1;
 			goto error;
 		}
 		delim = strchr(parentname, '@');
 		*delim = '\0';
 		zhrp = zfs_open(zhp->zfs_hdl, parentname, ZFS_TYPE_DATASET);
+		free(parentname);
 		if (zhrp == NULL) {
 			ret = -1;
 			goto error;
 		}
+		zfs_close(zhrp);
 	} else if (zhp->zfs_type != ZFS_TYPE_SNAPSHOT) {
 		if ((cl = changelist_gather(zhp, ZFS_PROP_NAME,
 		    CL_GATHER_ITER_MOUNTED,
@@ -4650,12 +4651,6 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive,
 	}
 
 error:
-	if (parentname != NULL) {
-		free(parentname);
-	}
-	if (zhrp != NULL) {
-		zfs_close(zhrp);
-	}
 	if (cl != NULL) {
 		changelist_free(cl);
 	}