staging: dgnc: unregister pci driver

We may choose to load the module without the hardware present. That will
register the pci driver but since probe will not succeed so
dgnc_NumBoards will be 0. Now if we unload the module then the pci
driver stays registered as dgnc_NumBoards is 0. And if we try to load
the module again it fails with the error:
"Driver 'dgnc' is already registered."
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_driver.c

@@ -156,8 +156,7 @@ static void dgnc_cleanup_module(void)
 
 	dgnc_tty_post_uninit();
 
-	if (dgnc_NumBoards)
-		pci_unregister_driver(&dgnc_driver);
+	pci_unregister_driver(&dgnc_driver);
 }
 
 /*