drivers/net/hamradio/6pack.c: move a dereference below a NULL test

In each case, if the NULL test is necessary, then the dereference should be
moved below the NULL test.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
type T;
expression E;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
  ... when != E
      when != i
  if (E == NULL) S
+ i = E->fld;
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/6pack.c

@@ -717,11 +717,12 @@ static int sixpack_ioctl(struct tty_struct *tty, struct file *file,
 	unsigned int cmd, unsigned long arg)
 {
 	struct sixpack *sp = sp_get(tty);
-	struct net_device *dev = sp->dev;
+	struct net_device *dev;
 	unsigned int tmp, err;
 
 	if (!sp)
 		return -ENXIO;
+	dev = sp->dev;
 
 	switch(cmd) {
 	case SIOCGIFNAME: