uml: drivers/net_user.c memory leak fix

Perform memory cleanup on exit.  On receiving invalid 'pid' we still
should clean 'output' variable.
Signed-off-by: NVitaliy Ivanov <vitalivanov@gmail.com>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/drivers/net_user.c

@@ -228,7 +228,10 @@ static void change(char *dev, char *what, unsigned char *addr,
 		       "buffer\n");
 
 	pid = change_tramp(argv, output, output_len);
-	if (pid < 0) return;
+	if (pid < 0) {
+		kfree(output);
+		return;
+	}
 
 	if (output != NULL) {
 		printk("%s", output);