usb: gadget: push iProduct into gadgets

This patch pushes the iProduct module argument from composite
into each gadget.

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>