Bluetooth: hci_qca: Fix driver shutdown on closed serdev

The driver shutdown callback (which sends EDL_SOC_RESET to the device
over serdev) should not be invoked when HCI device is not open (e.g. if
hci_dev_open_sync() failed), because the serdev and its TTY are not open
either.  Also skip this step if device is powered off
(qca_power_shutdown()).

Fixes: 7e7bbddd ("Bluetooth: hci_qca: Fix qca6390 enable failure after warm reboot")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>