usb: chipidea: add ci->is_otg condition for otg judgement

Since some chipidea based controller is not otg capable, add ci->is_otg
condition when setting is_otg flag for gadget.

Signed-off-by: Li Jun <jun.li@freescale.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>