Drop the lock before returning -EINVAL.

Fixes: ecaccdae ("wifi: mt76: mt7915: rework mt7915_thermal_temp_store()")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>