tpm2_policy: Do not overflow list of policy digests

[Vogtinator]

Don't try to write more digests into TPML_DIGEST than fit.

Otherwise this segfaults due to stack corruption:

fvogt-thinkpad:/tmp # tpm2_startauthsession -S session.ctx
fvogt-thinkpad:/tmp # tpm2_policypcr -S session.ctx -L p -l sha256:0
f5a83a2aa307e14029b7c910c90aaba705581ed582968babf64d7b4896abf16b
fvogt-thinkpad:/tmp # tpm2_policyor -S session.ctx -L policy.or sha256:p,p,p,p,p,p,p,p
e7200418d2f5510e111a4f48e2146414fc0bbc51adb9bd82b90870ec02bd97b3
fvogt-thinkpad:/tmp # tpm2_policyor -S session.ctx -L policy.or sha256:p,p,p,p,p,p,p,p,p
WARNING:marshal:src/tss2-mu/tpml-types.c:164:Tss2_MU_TPML_DIGEST_Marshal() count too big
ERROR:esys:src/tss2-esys/api/Esys_PolicyOR.c:177:Esys_PolicyOR_Async() SAPI Prepare returned error. ErrorCode (0x0008000b)
ERROR:esys:src/tss2-esys/api/Esys_PolicyOR.c:77:Esys_PolicyOR() Error in async function ErrorCode (0x0008000b)
ERROR: Esys_PolicyAuthorize(0x8000B) - sys:A parameter has a bad value
ERROR: Could not build policyor TPM
Segmentation fault (core dumped)