tracing: Replace deprecated strncpy() with strscpy() for stack_trace_filter_buf

strncpy() is deprecated for NUL-terminated destination buffers and must
be replaced by strscpy().

See issue: KSPP#90

Link: https://lore.kernel.org/20250507133837.19640-1-devaanshk840@gmail.com
Signed-off-by: Devaansh Kumar <devaanshk840@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: Devaansh-Kumar

kernel/trace/trace_stack.c

@@ -542,7 +542,7 @@ static __init int enable_stacktrace(char *str)
 	int len;
 
 	if ((len = str_has_prefix(str, "_filter=")))
-		strncpy(stack_trace_filter_buf, str + len, COMMAND_LINE_SIZE);
+		strscpy(stack_trace_filter_buf, str + len);
 
 	stack_tracer_enabled = 1;
 	return 1;