Bluetooth: Always use full path to hci_driver.h

The path to include/drivers should not be in the compiler include path
list, only include/. In order to make this possible, always explictly
refer to hci_driver.h via the drivers/bluetooth/ path and not only
bluetooth/.

Fixes #21974.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>