Bluetooth: hci_intel: Add check for platform_driver_register

As platform_driver_register() could fail, it should be better
to deal with the return value in order to maintain the code
consisitency.

Fixes: 1ab1f239 ("Bluetooth: hci_intel: Add support for platform driver")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>