Bluetooth: hci_qca: fix NULL pointer dereference in qca_setup() for non-serdev device

Bluetooth: hci_qca: fix NULL pointer dereference in qca_setup() for non-serdev device

hu->serdev is NULL for hci_uart attached via non-serdev paths, but
qca_setup() unconditionally calls serdev_device_get_drvdata(hu->serdev)
and dereferences the result, causing a NULL pointer dereference.

Fix by guarding the dereference with a NULL check, consistent with the
rest of qca_setup().

Fixes: 22d893eec0d5 ("Bluetooth: hci_qca: Refactor HFP hardware offload capability handling")
Signed-off-by: Zijun Hu <zijun.hu@oss.qualcomm.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>