wifi: mt76: mt7921: fix a potential scan no APs

wifi: mt76: mt7921: fix a potential scan no APs

In multi-channel scenarios, the granted channel must be aborted before
station remove. Otherwise, the firmware will be put into a wrong state,
resulting in have chance to make subsequence scan no APs.
With this patch, the granted channel will be always aborted before
station remove.

Signed-off-by: Quan Zhou <quan.zhou@mediatek.com>
Reviewed-by: Sean Wang <sean.wang@mediatek.com>
Tested-by: David Ruth <druth@chromium.org>
Reviewed-by: David Ruth <druth@chromium.org>
Link: https://patch.msgid.link/1ac1ae779db86d4012199a24ea2ca74050ed4af6.1721300411.git.quan.zhou@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>