Bluetooth: btusb: Fix potential NULL dereference on kmalloc failure

Avoid potential NULL pointer dereference by checking the return value of
kmalloc and handling allocation failure properly.

Fixes: 7d70989f ("Bluetooth: btusb: Add HCI Drv commands for configuring altsetting")
Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>