bin/util-linux.rs: use let/else instead of match

[cakebaker]

This PR uses let/else instead of match in two places.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (7f8d222) to head (41aace5).
⚠️ Report is 118 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #283   +/-   ##
===========================
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