VSOCK: Fix misc device registration

When we call vsock_core_init to init VSOCK the second time,
vsock_device.minor still points to the old dynamically allocated minor
number. misc_register will allocate it for us successfully as if we were
asking for a static one. However, when other user call misc_register to
allocate a dynamic minor number, it will give the one used by
vsock_core_init(), causing this:

  [  405.470687] WARNING: at fs/sysfs/dir.c:536 sysfs_add_one+0xcc/0xf0()
  [  405.470689] Hardware name: OptiPlex 790
  [  405.470690] sysfs: cannot create duplicate filename '/dev/char/10:54'

Always set vsock_device.minor to MISC_DYNAMIC_MINOR before we
register.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Andy King <acking@vmware.com>
Cc: Dmitry Torokhov <dtor@vmware.com>
Cc: Reilly Grant <grantr@vmware.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Asias He <asias@redhat.com>
Acked-by: Dmitry Torokhov <dtor@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/vmw_vsock/af_vsock.c

@@ -1932,7 +1932,6 @@ static const struct file_operations vsock_device_ops = {
 
 static struct miscdevice vsock_device = {
 	.name		= "vsock",
-	.minor		= MISC_DYNAMIC_MINOR,
 	.fops		= &vsock_device_ops,
 };
 
@@ -1942,6 +1941,7 @@ static int __vsock_core_init(void)
 
 	vsock_init_tables();
 
+	vsock_device.minor = MISC_DYNAMIC_MINOR;
 	err = misc_register(&vsock_device);
 	if (err) {
 		pr_err("Failed to register misc device\n");