storage: allow vold to access read_ahead_kb sysfs am: 17bf10575b am: 4c9c69f71f

Original change: https://android-review.googlesource.com/c/platform/hardware/google/pixel-sepolicy/+/2365529

Change-Id: I79b535a52de38e256fbed1d73a30bf178dc20aa1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>