staging: wilc1000: handle station dump cfg ops from cfg80211 context

Refactor code to handle dump_station() callback from cfg80211 context.
Instead of deferring issue of wid command now send it directly from cfg
context. Also making use of wilc_get_rssi() error status in case there
is a failure to post the wid command to the firmware.

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