staging: hv: Remove Ringbuffer from TODO line

Remove Ringbuffer work line item from TODO file.

The ring buffer in the Hyper-V Linux drivers is used to communicate with
the parent partition running Windows Server 2008 Hyper-V. The ring
buffer functionality on the Hyper-V Linux drivers is written to be
functionally compatible with the ring buffer functionality on the
Hyper-V Server. Consequently, it is not possible to make any changes
that might break the compatibility with server side ring buffer
implementation.

Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>