mt76: mt7921s: fix a possible memory leak in mt7921_load_patch

Always release fw data at the end of mt7921_load_patch routine.

Fixes: 78b21758 ("mt76: mt7921s: fix bus hang with wrong privilege")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>