ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

A use-after-free flaw was found in sndctlelemread in sound/core/control.c in Advanced Linux Sound Architecture ALSA subsystem in the Linux kernel. In this flaw a normal privileged, local attacker may impact the system due to a locking issue in the compat path, leading to a kernel information leak...