OpenZFS 9213 - zfs: sytem typo

Authored by: Toomas Soome <tsoome@me.com>
Reviewed by: C Fraire <cfraire@me.com>
Reviewed by: Andy Fiddaman <omnios@citrus-it.co.uk>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Approved by: Joshua M. Clulow <josh@sysmgr.org>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting Notes:

• The additional instances of this typo addressed in the OpenZFS patch were already resolved.

OpenZFS-issue: https://illumos.org/issues/9213
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/edc8ef7d92
Closes #7436