applicom: fix some err codes returned by ac_ioctl

When cmd > 6 or copy_to_user() fail, The variable 'ret' would not be
returned back. Fix the 'ret' set but not used.
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Xu Jia <xujia39@huawei.com>
Link: https://lore.kernel.org/r/20210324072031.941791-1-xujia39@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/applicom.c

@@ -839,7 +839,7 @@ static long ac_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	Dummy = readb(apbs[IndexCard].RamIO + VERS);
 	kfree(adgl);
 	mutex_unlock(&ac_mutex);
-	return 0;
+	return ret;
 
 err:
 	if (warncount) {