fix regression introduced in port of Illumos #3744

Don't call strfree on char array before use of char array as input parameter.

This fixes an upstream regression that was introduced in commit
zfsonlinux/zfs@d09f25dc66774959499a89bf3680d09c6e541ce8, which
ported the Illumos 3744 changes.

Signed-off-by: Andrey Vesnovaty <andrey.vesnovaty@gmail.com>