suspend_resume_single: clear pool errors on fail

If the timing is unfortunate, the pool can suspend just as we're failing
because it didn't suspend. If we don't resume the pool, we hang trying
to destroy it.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17054