Bluetooth: qca: Fix BT enable failure again for QCA6390 after warm reboot

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: qca: Fix BT enable failure again for QCA6390 after warm reboot Commit 272970be3dab ("Bluetooth: hci_qca: Fix driver shutdown on closed serdev") will cause below regression issue: BT can't be enabled after below steps: cold boot -> enable BT -> disable BT -> warm reboot -> BT enable failure if property enable-gpios is not configured within DT|ACPI for QCA6390. The commit is to fix a use-after-free issue within qca_serdev_shutdown() by adding condition to avoid the serdev is flushed or wrote after closed but also introduces this regression issue regarding above steps since the VSC is not sent to reset controller during warm reboot. Fixed by sending the VSC to reset controller within qca_serdev_shutdown() once BT was ever enabled, and the use-after-free issue is also fixed by this change since the serdev is still opened before it is flushed or wrote. Verified by the reported machine Dell XPS 13 9310 laptop over below two kernel commits: commit e00fc2700a3f ("Bluetooth: btusb: Fix triggering coredump implementation for QCA") of bluetooth-next tree. commit b23d98d46d28 ("Bluetooth: btusb: Fix triggering coredump implementation for QCA") of linus mainline tree.