usb: gadget: dummy_hcd: set gadget.is_otg before calling bind()

Before commit 53832daea ("usb: gadget: dummy_hcd: use the shared_hcd
infrastructure") the is_otg field was set in dummy_udc_probe(). It seems
to me that this field is used in gadget's bind function. Therefore I'm
moving it before the bind() callback is called.

Cc: Tatyana Brokhman <tlinder@codeaurora.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>