staging: wilc1000: change return type to 'void' for wilc_frame_register()

Cleanup patch to use 'void' return type for wilc_frame_register(), as
its return value is not used.

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