wifi: mt76: mt7925: fix stale pointer comparisons in change_vif_links

wifi: mt76: mt7925: fix stale pointer comparisons in change_vif_links

In the error path of mt7925_change_vif_links(), the free: label iterates
over link_ids to clean up, but compares against `mconf` and `mlink`
which hold stale values from the last loop iteration rather than the
current link_id being freed.

Use array-indexed access (mconfs[link_id] / mlinks[link_id]) to compare
against the correct per-link pointers.

Fixes: 69acd6d910b0 ("wifi: mt76: mt7925: add mt7925_change_vif_links")
Tested-by: Marcin FM <marcin@lgic.pl>
Tested-by: Cristian-Florin Radoi <radoi.chris@gmail.com>
Tested-by: George Salukvadze <giosal90@gmail.com>
Tested-by: Evgeny Kapusta <3193631@gmail.com>
Tested-by: Samu Toljamo <samu.toljamo@gmail.com>
Tested-by: Ariel Rosenfeld <ariel.rosenfeld.750@gmail.com>
Tested-by: Chapuis Dario <chapuisdario4@gmail.com>
Tested-by: Thibaut François <tibo@humeurlibre.fr>
Tested-by: 张旭涵 <Loong.0x00@gmail.com>
Reviewed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Javier Tia <floss@jetm.me>
Link: https://patch.msgid.link/20260425195011.790265-2-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>