kernel: Bluetooth: btbcm: Fix NULL deref in btbcm_get_board_name()

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: btbcm: Fix NULL deref in btbcmgetboardname devmkstrdup can return a NULL pointer on failure,but this returned value in btbcmgetboardname is not checked. Add NULL check in btbcmgetboardname, to handle kernel NULL pointe...