staging: wilc1000: handle error condition in add_key() and remove auth_type variable

Added the code to return correct error code in add_key() and also removed
'auth_type' variable. Now passing diretly to function instead of using
the 'auth_type' variable.

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>