Staging: hv: vmbus: Don't free the channel when the channel is closed

When the driver unloads, the device must persist. A channel represents the
device and so we should not free the channel when the channel is closed as
part of the driver unloading.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>