set_permissions: don't finish with exit code 1

That line made my Launchpad builds break. Not sure why this doesn't happen if I build the package on my PC.
```
chmod: cannot access '/usr/bin/notepadqq': No such file or directory
Makefile:787: recipe for target 'install_set_permissions' failed
make[2]: *** [install_set_permissions] Error 1
```