genfio: Protecting parse_cmdline from spaces

If you want to provide arguments with spaces in it, $@ shall be
protected with quotes.

That's required to manage complex cmdline for -A or -B options
diff --git a/tools/genfio b/tools/genfio
index 512313a..bbf8833 100755
--- a/tools/genfio
+++ b/tools/genfio
@@ -310,7 +310,7 @@
 
 ########## MAIN
 gen_template
-parse_cmdline $@
+parse_cmdline "$@"
 finish_template
 check_mode_order