usb: gadget: configfs: Fix complilation error

commit <237c1c19> ("usb: gadget: Bind android devices
for all UDC gadgets") caused compilation error when
CONFIG_USB_CONFIGFS_UEVENT is enabled.

Change-Id: Iafdd2463bdf99a20f2a7ed5f12d895c8ef6effaf
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>