EC_GROUP_cmp: add back the ignored BN_CTX arg

Change-Id: If7c25984fadcb98ea9fb26983e04b1be3b6a2ecd
diff --git a/src/crypto/ec/ec.c b/src/crypto/ec/ec.c
index 15e5735..30def15 100644
--- a/src/crypto/ec/ec.c
+++ b/src/crypto/ec/ec.c
@@ -491,7 +491,7 @@
   }
 }
 
-int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b) {
+int EC_GROUP_cmp(const EC_GROUP *a, const EC_GROUP *b, BN_CTX *ignored) {
   return a->curve_name == NID_undef ||
          b->curve_name == NID_undef ||
          a->curve_name != b->curve_name;