Fixed "widget-control.c:251:22: error: implicit declaration of function 'finish'

[ahysing]

Before

Link widget.elf
make[1]: Leaving directory `C:/Users/AHysing/code/sdr-widget/Release'
gcc -o widget-control widget-control.c -lusb-1.0
widget-control.c: In function 'setup':
widget-control.c:251:22: error: implicit declaration of function 'finish' [-Wimplicit-function-declaration]
  251 |                 exit(finish(1));
      |                      ^~~~~~
make: *** [widget-control] Error 1

After

make
./make-widget
make[1]: Entering directory `C:/Users/AHysing/code/sdr-widget/Release'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `C:/Users/AHysing/code/sdr-widget/Release'
gcc -o widget-control widget-control.c -lusb-1.0

Closes #4