tpm: Use auth only after NULL check in tpm_buf_check_hmac_response()

In the Linux kernel, the following vulnerability has been resolved: tpm: Use auth only after NULL check in tpm_buf_check_hmac_response() Dereference auth after NULL check in tpm_buf_check_hmac_response(). Otherwise, unless tpm2_sessions_init() was called, a call can cause NULL dereference, when TCG_TPM2_HMAC is enabled. [jarkko: adjusted the commit message.]