alim15x3: fix sparse warning

Fix this sparse warning:

  drivers/ide/alim15x3.c:594:2: warning: returning void-valued expression
Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/alim15x3.c

@@ -591,7 +591,7 @@ static int __init ali15x3_ide_init(void)
 
 static void __exit ali15x3_ide_exit(void)
 {
-	return pci_unregister_driver(&alim15x3_pci_driver);
+	pci_unregister_driver(&alim15x3_pci_driver);
 }
 
 module_init(ali15x3_ide_init);