tpm2_convert: fix EVP_EncodeUpdate usage for OSSL < 1.1.0
tpm2_convert: fix EVP_EncodeUpdate usage for OSSL < 1.1.0

Versions of OpenSSL less than 1.1.0 that have EVP_EncodeUpdate do not
return any value.

Fixes errors like:
lib/tpm2_convert.c: In function 'tpm2_base64_encode':
lib/tpm2_convert.c:658:8: error: void value not ignored as it ought to be
     rc = EVP_EncodeUpdate(ctx, out, &outl, buffer, buffer_length);
        ^

Signed-off-by: William Roberts <60148e894dabf0b83bde1d460768794cd453c455@intel.com>

01org/tpm2.0-tools,01org/tpm2.0-tools,01org/tpm2.0-tools