common/cmd_usb.c: fix warning: variable ... set but not used

Fix:
cmd_usb.c: In function 'usb_show_tree_graph':
cmd_usb.c:284:29: warning: variable 'port' set but not used [-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Remy Bohmer <linux@bohmer.net>
Acked-by: Remy Bohmer <linux@bohmer.net>

common/cmd_usb.c

@@ -281,7 +281,7 @@ static inline char *portspeed(int speed)
 void usb_show_tree_graph(struct usb_device *dev, char *pre)
 {
 	int i, index;
-	int has_child, last_child, port;
+	int has_child, last_child;
 
 	index = strlen(pre);
 	printf(" %s", pre);
@@ -300,7 +300,6 @@ void usb_show_tree_graph(struct usb_device *dev, char *pre)
 				/* found our pointer, see if we have a
 				 * little sister
 				 */
-				port = i;
 				while (i++ < dev->parent->maxchild) {
 					if (dev->parent->children[i] != NULL) {
 						/* found a sister */