tracing: Remove redundant 0 value initialization

The saved_cmdlines_buffer struct is already zeroed by memset(). It's
redundant to initialize s->cmdline_idx to 0.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250825123200.306272-1-liaoyuanhong@vivo.com


Signed-off-by: Liao Yuanhong <liaoyuanhong@vivo.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>