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: b1bba80a4376 ("vsock/vmci: register vmci_transport only when VMCI guest/host are active")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Mao Wenan <[e-mail]>
Reported-by: kbuild test robot <[e-mail]>
Signed-off-by: Stefano Garzarella <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/misc/vmw_vmci/vmci_driver.c

···
 
 static DEFINE_MUTEX(vmci_vsock_mutex); /* protects vmci_vsock_transport_cb */
 static vmci_vsock_cb vmci_vsock_transport_cb;
-bool vmci_vsock_cb_host_called;
+static bool vmci_vsock_cb_host_called;
 
 /*
  * vmci_get_context_id() - Gets the current context ID.