Fix format specifier warnings

Commit 5dbf6c5a66d did not address these format specifier warnings
since they were introduced by an unrelated commit which had not
been rebased on 5dbf6c5a66d when merged. Fix them.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #12435