mt76: mt7921: fix retrying release semaphore without end

We should pass the error code to the caller immediately
to avoid the possible infinite retry to release the semaphore.

Fixes: 1c099ab4 ("mt76: mt7921: add MCU support")
Co-developed-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: YN Chen <YN.Chen@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>