mesh: Fix mesh interface removal fix

mesh: Fix mesh interface removal fix

This wpa_drv_if_remove() call was previously modified to fix a different
issue, but that fix resulted in unconditional use of treed memory here
(wpa_supplicant_deinit_iface() frees wpa_s). Make a local copy of
wpa_s->parent to be able to use it after wpa_s is freed. The
mesh_if_created case has wpa_s->parent != wpa_s, so this should be
sufficient way of handling the wpa_drv_if_remove() call here.

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