library: add remaining changes for the new ECP_LIGHT symbol

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/oid.c b/library/oid.c
index 622e793..80cadcd 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -531,7 +531,7 @@
                         mbedtls_pk_type_t,
                         pk_alg)
 
-#if defined(MBEDTLS_ECP_C)
+#if defined(MBEDTLS_ECP_LIGHT)
 /*
  * For namedCurve (RFC 5480)
  */
@@ -621,7 +621,7 @@
                         oid_ecp_grp,
                         mbedtls_ecp_group_id,
                         grp_id)
-#endif /* MBEDTLS_ECP_C */
+#endif /* MBEDTLS_ECP_LIGHT */
 
 #if defined(MBEDTLS_CIPHER_C)
 /*