Constify ECDSA_METHOD_new.

PR#3920.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit aabd492320)

crypto/ecdsa/ecdsa.h

@@ -233,7 +233,7 @@ void *ECDSA_get_ex_data(EC_KEY *d, int idx);
  *  \return pointer to a ECDSA_METHOD structure or NULL if an error occurred
  */
 
-ECDSA_METHOD *ECDSA_METHOD_new(ECDSA_METHOD *ecdsa_method);
+ECDSA_METHOD *ECDSA_METHOD_new(const ECDSA_METHOD *ecdsa_method);
 
 /** frees a ECDSA_METHOD structure
  *  \param  ecdsa_method  pointer to the ECDSA_METHOD structure

crypto/ecdsa/ecs_lib.c

@@ -276,7 +276,7 @@ void *ECDSA_get_ex_data(EC_KEY *d, int idx)
     return (CRYPTO_get_ex_data(&ecdsa->ex_data, idx));
 }
 
-ECDSA_METHOD *ECDSA_METHOD_new(ECDSA_METHOD *ecdsa_meth)
+ECDSA_METHOD *ECDSA_METHOD_new(const ECDSA_METHOD *ecdsa_meth)
 {
     ECDSA_METHOD *ret;