staging: wilc1000: refactor wilc_netdev_init() to handle memory free in error path

Refactor the wilc_netdev_init() to cleanup the memory for error
scenario and remove unnecessary 'dev' pointer check.

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