Bluetooth: ISO: Fix bad chan pointer for disconnect
Bluetooth: ISO: Fix bad chan pointer for disconnect

If a central disconnects an ISO, then the `chan` pointer
will become NULL before attempting to call the
disconnect callback.

Signed-off-by: Emil Gydesen <a20314356615223738233ab4c4eb1cd8cd4146fa@nordicsemi.no>

galak/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr