pkarse: Update `pk_group_id_from_specified()` clean-up.

This path updates the clean-up logic of to individually
free each of the the group's structure members
rather than invoke `mbedtls_ecp_group_free()`.

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/library/pkparse.c b/library/pkparse.c
index 990b554..53e6dd0 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -429,7 +429,11 @@
     ret = pk_group_id_from_group(&grp, grp_id);
 
 cleanup:
-    mbedtls_ecp_group_free(&grp);
+    mbedtls_mpi_free(&grp.N);
+    mbedtls_mpi_free(&grp.P);
+    mbedtls_mpi_free(&grp.A);
+    mbedtls_mpi_free(&grp.B);
+    mbedtls_ecp_point_free(&grp.G);
 
     return ret;
 }