Staging: hv: vmbus: Use the newly introduced state in closing the channel

Now, use the newly introduced state in closing the channel and eliminate a
potential failure condition (that currently was not being handled correctly).

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>