stall-analyser: pass args.tmin instead of tmin

8e58341 introduced a regression, which passes an undefined variable of
`tmin` to `print_stats()`.

in this change, we pass `args.tmin` instead of `tmin` to this function.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes #2506

scripts/stall-analyser.py

@@ -442,7 +442,7 @@ def main():
             sys.exit()
         if args.format == 'graph':
             print_command_line_options(args)
-            print_stats(tally, tmin)
+            print_stats(tally, args.tmin)
         render.print_graph(args.direction, args.width, args.branch_threshold)
     except BrokenPipeError:
         pass