Fix GetSignatureDigestAlgorithm for openssl to prepare for EC key switch.
Fix GetSignatureDigestAlgorithm for openssl to prepare for EC key switch.

BUG=
R=davidben@chromium.org, juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/48209004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9061}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 01aeaee719a14f13304715f00628da4cb8660b30

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