usb: gadget: bcm63xx_udc: fix up the error of undeclared usb_debug_root

Fix up the build error caused by undeclared usb_debug_root

Cc: stable <stable@vger.kernel.org>
Fixes: a66ada4f24 ("usb: gadget: bcm63xx_udc: create debugfs directory under usb root")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/udc/bcm63xx_udc.c

@@ -26,6 +26,7 @@
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/timer.h>
+#include <linux/usb.h>
 #include <linux/usb/ch9.h>
 #include <linux/usb/gadget.h>
 #include <linux/workqueue.h>