tracing/histogram: Fix a potential memory leak for kstrdup()

kfree() is missing on an error path to free the memory allocated by
kstrdup():

  p = param = kstrdup(data->params[i], GFP_KERNEL);

So it is better to free it via kfree(p).

Link: https://lkml.kernel.org/r/[email protected]

Cc: [email protected]
Fixes: d380dcd ("tracing: Fix now invalid var_ref_vals assumption in trace action")
Signed-off-by: Xiaoke Wang <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: x2018

kernel/trace/trace_events_hist.c

@@ -3935,6 +3935,7 @@ static int trace_action_create(struct hist_trigger_data *hist_data,
 
 			var_ref_idx = find_var_ref_idx(hist_data, var_ref);
 			if (WARN_ON(var_ref_idx < 0)) {
+				kfree(p);
 				ret = var_ref_idx;
 				goto err;
 			}