[datagen] Remove extra newline printed

`datagen` was printing a `\n` even when it had no other output. Raise
the output level for the final `\n` to the minimum output level used.

This minor bug was caught by the new testing framework.

tests/datagencli.c

@@ -124,7 +124,7 @@ int main(int argc, const char** argv)
     DISPLAYLEVEL(3, "Seed = %u \n", (unsigned)seed);
 
     RDG_genStdout(size, (double)probaU32/100, litProba, seed);
-    DISPLAYLEVEL(1, "\n");
+    DISPLAYLEVEL(3, "\n");
 
     return 0;
 }