audioserver: grant read perms to /proc

In preparation of removing permissions from domain_deprecated.

Addresses:
avc: denied { read } for name="irq_affinity" dev="proc" ino=4026536760 scontext=u:r:audioserver:s0 tcontext=u:object_r:proc:s0 tclass=file
avc: denied { open } for path="/proc/asound/irq_affinity" dev="proc" ino=4026536760 scontext=u:r:audioserver:s0 tcontext=u:object_r:proc:s0 tclass=file
avc: denied { getattr } for path="/proc/asound/irq_affinity" dev="proc" ino=4026536760 scontext=u:r:audioserver:s0 tcontext=u:object_r:proc:s0 tclass=file

Change-Id: Iaa8843bb4e8b19d001520fcd45d35e666bf48271