usb: Drop use of BUG_ON() and WARN_ON()

These macros use __FILE__ which inserts the full path of the object file
into U-Boot, thus increasing file size. Drop these usages.

An older version of this patch was submitted here:

http://patchwork.ozlabs.org/patch/1205784/

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index c98a444..4a6f427 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1003,7 +1003,11 @@
 	 * so there's no i/o concurrency that could affect the
 	 * state protected by cdev->lock.
 	 */
+#ifdef __UBOOT__
+	assert_noisy(!cdev->config);
+#else
 	BUG_ON(cdev->config);
+#endif
 
 	while (!list_empty(&cdev->configs)) {
 		c = list_first_entry(&cdev->configs,