Upstream have added |EVP_PKEY_up_ref|, but their version returns an int.
Having this function with a different signature like that is dangerous
so this change aligns BoringSSL with upstream. Users of this function in
Chromium and internally should already have been updated.
Change-Id: I0a7aeaf1a1ca3b0f0c635e2ee3826aa100b18157
Reviewed-on: https://boringssl-review.googlesource.com/8736
Reviewed-by: David Benjamin <davidben@google.com>