Bluetooth: btusb: Fix application of sizeof to pointer

The coccinelle check report:
"./drivers/bluetooth/btusb.c:2239:36-42:
ERROR: application of sizeof to pointer".
Using the real size to fix it.

Fixes: 5a87679f

 ("Bluetooth: btusb: Support public address configuration for MediaTek Chip.")
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: David Yang <davidcomponentone@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>