brcmsmac: delete useless variable

Delete a variable that is at most only assigned to a constant, but never
used otherwise.

A simplified version of the semantic patch that fixes this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
type T;
identifier i;
constant c;
@@

-T i;
<... when != i
-i = c;
...>
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>