Bluetooth: btnxpuart: Fix use-after-free in probe error path

In nxp_serdev_probe(), if hci_register_dev() succeeds but ps_setup()
fails, the error path jumps to 'probe_fail' which only calls
hci_free_dev() and asserts the reset GPIO, but does NOT call
hci_unregister_dev() first.

This leaves the HCI device registered in the system with its backing
memory freed, leading to a use-after-free when userspace subsequently
accesses the device (e.g. via hciconfig or bluetoothd).

Fix by adding a 'probe_fail_unregister' label that calls
hci_unregister_dev() before falling through to the existing
'probe_fail' label. The original 'probe_fail' label is preserved
for the case where hci_register_dev() itself fails (device was
never registered, so no unregister is needed).

Signed-off-by: Zhao Dongdong <zhaodongdong@kylinos.cn>
Reviewed-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>