usb: musb: gadget: remove hcd initialization

This will be done from a more appropriate location and as it doesn't
work anyway, it can safely be removed before the other changes.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Felipe Balbi <balbi@ti.com>