tpm2-util: rename tpm2_get_pin_auth() → tpm2_auth_value_from_pin()

Just some renaming. I found the old name a bit confusing since it sounds
as if this would get the pin from somewhere, but it really doesn't. It
just converts a PIN into an auth_value, and I think saying so explicitly
makes things easier to grok.

src/pcrlock/pcrlock.c

@@ -4500,7 +4500,7 @@ static int make_policy(bool force, bool recovery_pin) {
         CLEANUP_ERASE(auth);
 
         if (pin) {
-                r = tpm2_get_pin_auth(TPM2_ALG_SHA256, pin, &auth);
+                r = tpm2_auth_value_from_pin(TPM2_ALG_SHA256, pin, &auth);
                 if (r < 0)
                         return log_error_errno(r, "Failed to hash PIN: %m");
         } else {