idpf: nullify pointers after they are freed

commit bc3b319 upstream.

rss_data->rss_key needs to be nullified after it is freed.
Checks like "if (!rss_data->rss_key)" in the code could fail
if it is not nullified.

Tested: built and booted the kernel.

Fixes: 83f38f2 ("idpf: Fix RSS LUT NULL pointer crash on early ethtool operations")
Signed-off-by: Li Li <boolli@google.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Samuel Salin <Samuel.salin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Li Li

drivers/net/ethernet/intel/idpf/idpf_lib.c

@@ -1230,6 +1230,7 @@ static struct idpf_vport *idpf_vport_alloc(struct idpf_adapter *adapter,
 
 free_rss_key:
 	kfree(rss_data->rss_key);
+	rss_data->rss_key = NULL;
 free_vector_idxs:
 	kfree(vport->q_vector_idxs);
 free_vport: