wifi: mt76: mt792x: fix mt7925u USB WFSYS reset handling

wifi: mt76: mt792x: fix mt7925u USB WFSYS reset handling

mt7925u uses different reset/status registers from mt7921u. Reusing the
mt7921u register set causes the WFSYS reset to fail.

Add a chip-specific descriptor in mt792xu_wfsys_reset() to select the
correct registers and fix mt7925u failing to initialize after a warm
reboot.

Fixes: d28e1a48952e ("wifi: mt76: mt792x: introduce mt792x-usb module")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260311002825.15502-2-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>