net: phy: ncsi: fixed not nullify the pointers after free

The issue occurs the UAF (use-after-free) to cause double free
when do the realloc function for the pointers during the
reinitialization NC-SI process, and it will cause the memory
management occurs error.
So, nullify these pointers after free.

Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
diff --git a/drivers/net/phy/ncsi.c b/drivers/net/phy/ncsi.c
index eb3fd65..9689385 100644
--- a/drivers/net/phy/ncsi.c
+++ b/drivers/net/phy/ncsi.c
@@ -619,9 +619,12 @@
 
 	/* Link or configuration lost - just redo the discovery process */
 	ncsi_priv->state = NCSI_PROBE_PACKAGE_SP;
-	for (i = 0; i < ncsi_priv->n_packages; i++)
+	for (i = 0; i < ncsi_priv->n_packages; i++) {
 		free(ncsi_priv->packages[i].channels);
+		ncsi_priv->packages[i].channels = NULL;
+	}
 	free(ncsi_priv->packages);
+	ncsi_priv->packages = NULL;
 	ncsi_priv->n_packages = 0;
 
 	ncsi_priv->current_package = NCSI_PACKAGE_MAX;