wifi: mt76: mt7925: prevent multiple scan commands

Add a check to ensure only one scan command is active at a time
by testing the MT76_HW_SCANNING state.

Fixes: c948b5da ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Link: https://patch.msgid.link/20250414013954.1151774-1-mingyen.hsieh@mediatek.com


Signed-off-by: Felix Fietkau <nbd@nbd.name>