staging: wilc1000: assign scan result callback before starting the scan

When scan is triggered, sometimes scan results are received before the scan
result callback is assigned, causing the recieved results to be ignored.

Signed-off-by: Adham Abozaeid <adham.abozaeid@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>