drivers/net/wireless/libertas: 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.  I have also taken advantage of the availability
of the value of priv->dev in the subsequent calls to netif_stop_queue and
netif_carrier_off.

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>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>