staging: wilc1000: handle scan operation callback from cfg80211 context

Refactor code to handle scan operation callback from cfg80211 context.
No need to maintain 'scan_attr' struct as the wid command is directly
sent to firmware from cfg80211 context.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>