iw: avoid passing NULL to nla_data()
iw: avoid passing NULL to nla_data()

The attr pointer is checked for NULL but the function
doesn't handle it appropriately - fix that.

Signed-off-by: Amit Khatri <34a5a3eacdf43e9bbefea5937322e2586e63a8b5@samsung.com>
Signed-off-by: Rahul Jain <d63d72e13bea5c92e4971ea5538badba5f0d7d11@samsung.com>
Signed-off-by: Johannes Berg <bff32994ff0f8d048f262a8388145a71b6071bfe@intel.com>

bw-oss/iw,greearb/iw-ct,bw-oss/iw,greearb/iw-ct