vtls: Use CURLcode for Curl_ssl_init_certinfo() return type

vtls: Use CURLcode for Curl_ssl_init_certinfo() return type

The return type for this function was 0 on success and 1 on error. This
was then examined by the calling functions and, in most cases, used to
return CURLE_OUT_OF_MEMORY.

Instead use CURLcode for the return type and return the out of memory
error directly, propagating it up the call stack.