Bluetooth: btmtksdio: Add the missed release_firmware() in mtk_setup_firmware()

mtk_setup_firmware() misses to call release_firmware() in an error
path. Jump to free_fw to fix it.

Fixes: 737cd060 ("Bluetooth: btmtksdio: fix up firmware download sequence")
Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>