staging: wilc1000: handle freeing of key data in wep add key

Modified the code to free the allocated memory, used to store the key in
wilc_add_wep_key_bss_sta() and wilc_add_wep_key_bss_ap().
After work completion notification is received, free the
memory allocated 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>