Remove ecdh_ctx variable, init & free when USE_PSA_CRYPTO isn't selected

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 66fae92..90fa686 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -626,7 +626,7 @@
 #if defined(MBEDTLS_DHM_C)
     mbedtls_dhm_init( &handshake->dhm_ctx );
 #endif
-#if defined(MBEDTLS_ECDH_C)
+#if !defined(MBEDTLS_USE_PSA_CRYPTO) && defined(MBEDTLS_ECDH_C)
     mbedtls_ecdh_init( &handshake->ecdh_ctx );
 #endif
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
@@ -3134,7 +3134,7 @@
 #if defined(MBEDTLS_DHM_C)
     mbedtls_dhm_free( &handshake->dhm_ctx );
 #endif
-#if defined(MBEDTLS_ECDH_C)
+#if !defined(MBEDTLS_USE_PSA_CRYPTO) && defined(MBEDTLS_ECDH_C)
     mbedtls_ecdh_free( &handshake->ecdh_ctx );
 #endif
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)