Bluetooth: hci_ll: Fix firmware leak on error path

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_ll: Fix firmware leak on error path Smatch reports: drivers/bluetooth/hci_ll.c:587 download_firmware() warn: 'fw' from request_firmware() not released on lines: 544. In download_firmware(), if request_firmware() succeeds but the returned firmware content is invalid (no data or zero size), the function returns without releasing the firmware, resulting in a resource leak. Fix this by calling release_firmware() before returning when request_firmware() succeeded but the firmware content is invalid.