Previously, probe_superblocks() forwarded blkid_do_fullprobe()'s and
blkid_do_safeprobe()'s raw return code on error, which is just -1 with
no errno attached. The caller passes this value straight to
log_device_debug_errno() with %m, so a generic probing failure always
printed strerror(-1) regardless of what actually went wrong.
Convert the -1 error case to a proper negative errno via
errno_or_else(), matching the pattern used elsewhere in this file. The
'nothing found' (1) and success (0) return values are unchanged.
Daniel28972897
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