staging: wilc1000: refactor scan() to free kmalloc memory on failure cases

Added changes to free the allocated memory in scan() for error condition.
Also added 'NULL' check validation before accessing allocated memory.
Copied the SSID information in consecutive slots to avoid inbetween
holes while filling into array.

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