[v5] Bluetooth: hci_uart: fix UAF in hci_uart_tty_close()

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16: B1 Line exceeds max length (124>80): "  ODEBUG: free active (active state 0) object: ffff88804024e870 object type: work_struct hint: hci_uart_write_work+0x0/0x940"
17: B1 Line exceeds max length (86>80): "  WARNING: CPU: 0 PID: 338273 at lib/debugobjects.c:612 debug_print_object+0x1a2/0x2b0"
57: B2 Line has trailing whitespace: "- Moved disable_work_sync() to the very top of hci_uart_tty_close(), "
58: B2 Line has trailing whitespace: "  before hci_uart_close(), to prevent any concurrent re-queuing "
62: B2 Line has trailing whitespace: "- Adopted Luiz's suggestion to use disable_work_sync() instead of "