wifi: mt76: mt7921: resource leaks at mt7921_check_offload_capability()

Fixed coverity issue with resource leaks at variable "fw" going out of
scope leaks the storage it points to mt7921_check_offload_capability().

Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527806 ("Resource leaks")
Fixes: 034ae28b ("wifi: mt76: mt7921: introduce remain_on_channel support")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>