udev rules: avoid spurious warning for non-SCSI devices

[mwilck]

The udev rules spit out lots of warnings like this:

55-scsi-sg3_id.rules[15445]: WARNING: SCSI device loop0 has no device ID, consider changing .SCSI_ID_SERIAL_SRC in 00-scsi-sg3_config.rules

Because the warning code had erroneously been inserted in the "sg3_utils_id_end" clause. Fix it.

Fixes: d7b8da0 ("udev rules: restrict use of ambiguous device IDs patchset")

[mwilck]

@doug-gilbert, please review and apply. This fixes annoying warnings for lots of block devices.