wifi: rtw89: mcc: drop queued chanctx changes when stopping

When MCC is about to stop, there may be some chanctx changes which are
queued for work but have not yet been run. To avoid these changes from
being processed in a wrong state (e.g. next new MCC instance), cancel
the queued work and drop queued changes.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250511035217.10410-3-pkshih@realtek.com