staging: wilc1000: handle freeing of 'key' & 'seq' data in wilc_add_rx_gtk()

Handle freeing of memory allocated to keep 'key' & 'seq' in wilc_add_rx_gtk().
Once completion event is received, free the memory allocated for
to avoid missing of free in work function.

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