Free P and N of the group cause they are dynamic allocated

Signed-off-by: Xiaokang Qian <xiaokang.qian@arm.com>
diff --git a/library/ecp.c b/library/ecp.c
index 049a1e0..15da4a2 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -591,9 +591,11 @@
     }
 
     if (grp->h != 1) {
+        mbedtls_mpi_free(&grp->P);
         mbedtls_mpi_free(&grp->A);
         mbedtls_mpi_free(&grp->B);
         mbedtls_ecp_point_free(&grp->G);
+        mbedtls_mpi_free(&grp->N);
     }
 
     if (!ecp_group_is_static_comb_table(grp) && grp->T != NULL) {