PCI: hv: Don't leak buffer in hv_pci_onchannelcallback()

We don't free buffer on several code paths in hv_pci_onchannelcallback(),
put kfree() to the end of the function to fix the issue.  Direct { kfree();
return; } can now be replaced with a simple 'break';

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jake Oshins <jakeo@microsoft.com>