[WATCHDOG] pcwd_usb.c: fix a NULL pointer dereference

The Coverity checker noted that this resulted in a NULL pointer
reference if we were coming from

if (usb_pcwd == NULL) {
printk(KERN_ERR PFX "Out of memory\n");
goto error;
}

Signed-off-by: Adrian Bunk <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/char/watchdog/pcwd_usb.c

···
 err_out_unregister_reboot:
 	unregister_reboot_notifier(&usb_pcwd_notifier);
 error:
-	usb_pcwd_delete (usb_pcwd);
+	if (usb_pcwd)
+		usb_pcwd_delete(usb_pcwd);
 	usb_pcwd_device = NULL;
 	return retval;
 }