Fix guards around use of legacy ECDH context

mbedtls_ssl_handshake_params::ecdh_ctx should only be guarded
by MBEDTLS_ECDH_C, not by MBEDTLS_ECDSA_C.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 0488f7b..478b208 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1404,7 +1404,7 @@
         if( p[0] == MBEDTLS_ECP_PF_UNCOMPRESSED ||
             p[0] == MBEDTLS_ECP_PF_COMPRESSED )
         {
-#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
+#if defined(MBEDTLS_ECDH_C)
             ssl->handshake->ecdh_ctx.point_format = p[0];
 #endif
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)