Revert "OPP: add index check to assert to avoid buffer overflow in _read_freq()"

This reverts commit 774dd6f0 which is
commit d659bc68 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I6295c420bb6642fb9f04770a9f3baefa2d0aee72
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>