hamradio/mkiss: fix typo in compat_ioctl

My last commit introduced an typo causing the
compat_ioctl function to do nothing useful.
The obvious way for an ioctl function to work
is to look at the command, not the argument first.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/mkiss.c

@@ -903,7 +903,7 @@ static int mkiss_ioctl(struct tty_struct *tty, struct file *file,
 static long mkiss_compat_ioctl(struct tty_struct *tty, struct file *file,
 	unsigned int cmd, unsigned long arg)
 {
-	switch (arg) {
+	switch (cmd) {
 	case SIOCGIFNAME:
 	case SIOCGIFENCAP:
 	case SIOCSIFENCAP: