tpm: Don't log duplicate identical events

tpm: Don't log duplicate identical events

According to the comment in tpm_measure_variable ("Don't measure something that we've already measured"), shim
shouldn't measure duplicate events if they are identical, which also aligns with section 2.3.4.8 of the TCG PC
Client Platform Firmware Profile Specification ("If it has been measured previously, it MUST NOT be measured
again"). This is currently broken because tpm_data_measured() uses the return value of CompareGuid() incorrectly.

Upstream-commit-id: 103adc89ce5