wifi: mt76: mt7925: fix invalid array index in ssid assignment during hw scan

wifi: mt76: mt7925: fix invalid array index in ssid assignment during hw scan

Update the destination index to use 'n_ssids', which is incremented only
when a valid SSID is present. Previously, both mt76_connac_mcu_hw_scan()
and mt7925_mcu_hw_scan() used the loop index 'i' for the destination
array, potentially leaving gaps if any source SSIDs had zero length.

Cc: stable@vger.kernel.org
Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Michael Lo <michael.lo@mediatek.com>
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Link: https://patch.msgid.link/20250612062046.160598-1-mingyen.hsieh@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>