Bluetooth: btusb: Handle download_firmware failure cases

For Mediatek chipset, it can not enabled if there are something wrong
in btmtk_setup_firmware_79xx(). Thus, the process must be terminated
and returned error code.

Fixes: fc342c4d ("Bluetooth: btusb: Add protocol support for MediaTek MT7921U USB devices")
Co-developed-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Mark Chen <mark-yw.chen@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/btusb.c

@@ -2633,6 +2633,10 @@ static int btusb_mtk_setup(struct hci_dev *hdev)
 			 dev_id & 0xffff, (fw_version & 0xff) + 1);
 		err = btmtk_setup_firmware_79xx(hdev, fw_bin_name,
 						btusb_mtk_hci_wmt_sync);
+		if (err < 0) {
+			bt_dev_err(hdev, "Failed to set up firmware (%d)", err);
+			return err;
+		}
 
 		/* It's Device EndPoint Reset Option Register */
 		btusb_mtk_uhw_reg_write(data, MTK_EP_RST_OPT, MTK_EP_RST_IN_OUT_OPT);