BugLink: https://launchpad.net/bugs/1712746

Check priv->wdev.wiphy before dereference.
Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-By: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>