USB: gadget: Fix error path in ci13xxx_udc gadget probe function

Don't call gadget driver's unbind when bind is failed.  Initialize
udc->driver only after gadget driver bind is successful.  Otherwise
pull-up can be enabled upon VBUS session even when no gadget is
bounded.

Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>