Bluetooth: btrtl: check for NULL in btrtl_setup_realtek()

If insert an USB dongle which chip is not maintained in ic_id_table, it
will hit the NULL point accessed. Add a null point check to avoid the
Kernel Oops.

Fixes: b39910bb ("Bluetooth: Populate hci_set_hw_info for Intel and Realtek")
Reviewed-by: Alex Lu <alex_lu@realsil.com.cn>
Signed-off-by: Max Chou <max.chou@realtek.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>