pktgen: Fix memory leak in pktgen_if_write

_buf_ is an array and the one that must be freed is _tp_ instead.

Fixes: a870a02c ("pktgen: use dynamic allocation for debug print buffer")
Reported-by: Wang Jian <jianjian.wang1@gmail.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -913,7 +913,7 @@ static ssize_t pktgen_if_write(struct file *file,
 			return PTR_ERR(tp);
 
 		pr_debug("%s,%zu  buffer -:%s:-\n", name, count, tp);
-		kfree(buf);
+		kfree(tp);
 	}
 
 	if (!strcmp(name, "min_pkt_size")) {