scan: wps: fix some misplaced code
scan: wps: fix some misplaced code

I added a length check, but neglected to move the actual
data access after that ... fix that!

Change-Id: I6cf3f396ce86c70df0d1f917b6a028de657ff2a7
Signed-off-by: Johannes Berg <bff32994ff0f8d048f262a8388145a71b6071bfe@intel.com>

greearb/iw-ct,greearb/iw-ct