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

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

Change-Id: I634387c18d259ac7c50645afeafd9fe1f862e9b9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>