CVE-2023-52904 ALSA: usb-audio: Fix possible NULL pointer dereference in snd_usb_pcm_has_fixed_rate()

In the Linux kernel, the following vulnerability has been resolved: ALSA: usb-audio: Fix possible NULL pointer dereference in sndusbpcmhasfixedrate The subs function argument may be NULL, so do not use it before the NULL check...