Suppress missing return value check warning in |EVP_DigestFinal|.

This is harmless, but it wasn't annoted with |(void)| so Coverity
complained about it.

Change-Id: Ie3405b0c0545944d49973d4bf29f8aeb6b965211
Reviewed-on: https://boringssl-review.googlesource.com/5612
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

crypto/digest/digest.c

diff --git a/crypto/digest/digest.c b/crypto/digest/digest.c
index 7082c48..ada1166 100644
--- a/crypto/digest/digest.c
+++ b/crypto/digest/digest.c
@@ -203,7 +203,7 @@
 }
 
 int EVP_DigestFinal(EVP_MD_CTX *ctx, uint8_t *md, unsigned int *size) {
-  EVP_DigestFinal_ex(ctx, md, size);
+  (void)EVP_DigestFinal_ex(ctx, md, size);
   EVP_MD_CTX_cleanup(ctx);
   return 1;
 }