vsock/vmci: make vmci_vsock_cb_host_called static

When using make C=2 drivers/misc/vmw_vmci/vmci_driver.o
to compile, below warning can be seen:
drivers/misc/vmw_vmci/vmci_driver.c:33:6: warning:
symbol 'vmci_vsock_cb_host_called' was not declared. Should it be static?

This patch make symbol vmci_vsock_cb_host_called static.

Fixes: b1bba80a ("vsock/vmci: register vmci_transport only when VMCI guest/host are active")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>