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

Use 'void' return type for wilc_wfi_deinit_mon_interface(), as same
value always return.

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