Revert "ring-buffer: Fix wrong stat of cpu_buffer->read"

This reverts commit 23e8a65f which is
commit 2d093282 upstream.

It breaks the Android abi and isn't really needed for Android systems.
If it is needed in the future, it can come back in an ABI-safe way.

Bug: 161946584
Change-Id: I1def9966078008125f445941af21e518617a0011
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>