drivers/net/wireless/mwifiex/scan.c: test the just-initialized value

Test the just-initialized value rather than some other one.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r@
identifier x,y,f!={PTR_ERR,ERR_PTR,ERR_CAST};
statement S;
@@

x = f(...);
(
if (\(x == NULL\|IS_ERR(x)\)) S
|
*if (\(y == NULL\|IS_ERR(y)\))
 { ... when != x
   return ...; }
)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Acked-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>