usb: gadget: dummy: fix infinite loop because of missing loop decrement

The while loop never terminates because the loop counter i is never
decremented. Fix this by decrementing i.

Detected by CoverityScan, CID#751073 ("Infinite Loop")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/dummy_hcd.c

@@ -2776,7 +2776,7 @@ static int __init init(void)
 		if (retval < 0) {
 			i--;
 			while (i >= 0)
-				platform_device_del(the_udc_pdev[i]);
+				platform_device_del(the_udc_pdev[i--]);
 			goto err_add_udc;
 		}
 	}