cdc-acm: Destroy acm_minors IDR on module exit

Destroy acm_minors IDR on module exit, reclaiming the allocated memory.

This was detected by the following semantic patch (written by Luis Rodriguez
<mcgrof@suse.com>)
<SmPL>
@ defines_module_init @
declarer name module_init, module_exit;
declarer name DEFINE_IDR;
identifier init;
@@

module_init(init);

@ defines_module_exit @
identifier exit;
@@

module_exit(exit);

@ declares_idr depends on defines_module_init && defines_module_exit @
identifier idr;
@@

DEFINE_IDR(idr);

@ on_exit_calls_destroy depends on declares_idr && defines_module_exit @
identifier declares_idr.idr, defines_module_exit.exit;
@@

exit(void)
{
 ...
 idr_destroy(&idr);
 ...
}

@ missing_module_idr_destroy depends on declares_idr && defines_module_exit && !on_exit_calls_destroy @
identifier declares_idr.idr, defines_module_exit.exit;
@@

exit(void)
{
 ...
 +idr_destroy(&idr);
 }
</SmPL>

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Acked-by: Oliver Neukum <oneukum@suse.com>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -1944,6 +1944,7 @@ static void __exit acm_exit(void)
 	usb_deregister(&acm_driver);
 	tty_unregister_driver(acm_tty_driver);
 	put_tty_driver(acm_tty_driver);
+	idr_destroy(&acm_minors);
 }
 
 module_init(acm_init);