net: ipw2x00: Replace NULL comparison with !priv

Remove extra parentheses and replace NULL comparison with !priv, to fix
clang warning of extraneous parentheses and check patch issue. Following
coccinelle script is used to fix it.

@disable is_null,paren@
expression e;
statement s;
@@
if (
- (e==NULL)
+!e
 )
s

Signed-off-by: Varsha Rao <rvarsha016@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>