staging: wilc1000: avoid deferred handling of cfg80211 disconnect callback

Refactor disconnect operation callback to handle from the cfg80211
context. The reason code is not required to pass as parameter to the
function, so remove it.

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