[PATCH v1] wifi: mt76: mt7925: Fix MCU command timeouts during module unload

[Devin Wittmayer]

Tested this on an MT7927 here, against a reproduction I built on
2026-08-02 when I hit the same teardown. It fixes it.

mt7925e on 7.1.5, morrownr/mt76 at 217ee83d, which carries the
unregister-deadlock change your Fixes tag names (openwrt 98c13eb564e5).
Each cycle associates WPA2 at 2412 MHz, runs a 1400-byte ICMP flood, and
rmmods with that traffic in flight, RX sampled off statistics/rx_packets
immediately before the unload at 375 to 807 pps across both arms. Both
arms built in the same directory, so only mt7925e and mt792x_lib differ
between them.

  condition              stock                      patched
  associated, 10 cycles  59-60 s, 19 timeouts each  0-1 s, none
  idle, 3 cycles         9-10 s, 3 timeouts each    0 s, none

No warnings or call traces in any window on either arm.

The idle row is worth a line in the commit message: with nothing
associated it still costs 9 to 10 seconds, so a bare rmmod does reach
this, just small enough there to read as normal teardown.

Tested-by: Devin Wittmayer <lucid_duck at justthetip.ca>