Fix unchecked return values

2a493a4c7127258b14c39e8c71a9d6f01167c5cd was intended to fix all
instances of coverity reported unchecked return values, but
unfortunately, two were missed by mistake. This commit fixes the
unchecked return values that had been missed.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Neal Gompa <ngompa@datto.com>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13945