tools/virtiofsd/fuse_lowlevel: Fix fuse_out_header::error value

tools/virtiofsd/fuse_lowlevel: Fix fuse_out_header::error value

Fix warning reported by Clang static code analyzer:

    CC      tools/virtiofsd/fuse_lowlevel.o
  tools/virtiofsd/fuse_lowlevel.c:195:9: warning: Value stored to 'error' is never read
          error = -ERANGE;
          ^       ~~~~~~~

Fixes: 3db2876
Reported-by: Clang Static Analyzer
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>