ALSA: usx2y: us144mkii: fix NULL deref on missing interface 0

In the Linux kernel, the following vulnerability has been resolved: ALSA: usx2y: us144mkii: fix NULL deref on missing interface 0 A malicious USB device with the TASCAM US-144MKII device id can have a configuration containing bInterfaceNumber=1 but no interface 0. USB configuration descriptors are not required to assign interface numbers sequentially, so usb_ifnum_to_if(dev, 0) returns will NULL, which will then be dereferenced directly. Fix this up by checking the return value properly.