acpidump(8) Fix typo in error message

acpidump(8) uses iasl(8) to parse acpi information.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D44596

(cherry picked from commit 861f5b95b39fd8a6b10b7bddf29e284e5ba2c49a)