fix(rv_timer): Fix trailing whitespace

Revise `reg_timer.py` to strip the trailing newline

Signed-off-by: Eunchan Kim <eunchan@opentitan.org>
diff --git a/hw/ip/rv_timer/util/reg_timer.py b/hw/ip/rv_timer/util/reg_timer.py
index 4209060..2797e95 100755
--- a/hw/ip/rv_timer/util/reg_timer.py
+++ b/hw/ip/rv_timer/util/reg_timer.py
@@ -36,7 +36,7 @@
     out = StringIO()
 
     reg_tpl = Template(args.input.read())
-    out.write(reg_tpl.render(harts=args.harts, timers=args.timers))
+    out.write(reg_tpl.render(harts=args.harts, timers=args.timers).rstrip())
 
     print(out.getvalue())