In case of invalid sub channel, release cpu lock before returning.

Fixes: a949e86c ("Drivers: hv: vmbus: Resolve race between init_vp_index() and CPU hotplug")
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1654794996-13244-1-git-send-email-ssengar@linux.microsoft.comSigned-off-by: Wei Liu <wei.liu@kernel.org>