trivial: dell: work around a memory leak caught by address sanitizer
trivial: dell: work around a memory leak caught by address sanitizer

It appears to only happen on non-dell systems trying to look up system
ID through `sysinfo_get_dell_system_id`

Other than CI non-dell systems won't be running this code.

fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd