P2P: Fix interface deinit for failed group interface initialization

P2P: Fix interface deinit for failed group interface initialization

wpa_supplicant_deinit_iface() ends up removing all P2P groups if the
removed interface is the parent interface. This is correct behavior in
general, but this resulted in issues in the new group interface
initialization error path since wpa_s->parent was not assigned before
hitting this check. Fix this by assigning wpa_s->parent as part of
wpa_supplicant_add_iface().

Signed-off-by: Jouni Malinen <j@w1.fi>