verification/dot2k: Remove __buff_to_string()

verification/dot2k: Remove __buff_to_string()

str.join() can do what __buff_to_string() does. Therefore replace
__buff_to_string() to make the scripts more pythonic.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/860d6002659f604c743e0f23d5cf3c99ea6a82d8.1751634289.git.namcao@linutronix.de
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>