commit fc96df16a1ce80cbb3c316ab7d4dc8cd5c2852ce upstream.

Before 98f4c651, we returned zeros for unopened channels.
With 98f4c651, we started to return random on-stack values.

We'd better return -EINVAL instead.

Fixes: 98f4c651 ("hv: move ringbuffer bus attributes to dev_groups")
Cc: stable@vger.kernel.org
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: NDexuan Cui <decui@microsoft.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>