RMX1921: sepolicy: Allow qti_init_shell to write to read_ahead_kb

* avc: denied { write } for pid=4565 comm="init.qcom.post_" name="read_ahead_kb" dev="sysfs" ino=52742 scontext=u:r:qti_init_shell:s0 tcontext=u:object_r:sysfs:s0 tclass=file

Change-Id: I3e5350eb67aa9a0e539d74c2ecbd7114e03ffdc5