ssl_tls13: use PSA_WANT_ALG_ECDH as symbol for marking ECDH capability

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 1572bcd..38077dd 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1428,7 +1428,7 @@
     return ret;
 }
 
-#if defined(MBEDTLS_PK_CAN_ECDH)
+#if defined(PSA_WANT_ALG_ECDH)
 
 int mbedtls_ssl_tls13_read_public_ecdhe_share(mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
@@ -1510,7 +1510,7 @@
 
     return 0;
 }
-#endif /* MBEDTLS_PK_CAN_ECDH */
+#endif /* PSA_WANT_ALG_ECDH */
 
 /* RFC 8446 section 4.2
  *