sd-id128: make sd_id128_get_machine() or friends return -EUCLEAN when an ID is in...

sd-id128: make sd_id128_get_machine() or friends return -EUCLEAN when an ID is in an invalid format

EINVAL suggests that the caller passes an invalid argument. EIO is
for "input/output error", i.e. the error you'd get if the disk or
file system is borked, and this error code could be returned by the
underlying read/write functions.

Let's make the functions return an unambiguous error code.