usb: chipidea: imx: avoid EPROBE_DEFER printed as error

Avoid printing an error if adding the device failes with return
value EPROBE_DEFFER. This may happen e.g. due to missing GPIO for
the vbus-supply regulator.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Peter Chen <peter.chen@nxp.com>