USB: fsl_udc_core: use usb_endpoint_xfer_isoc to judge ISO XFER

Some ISO gadgets, like audio, has SYNC attribute as well as
USB_ENDPOINT_XFER_ISOC for their bmAttributes at ISO endpoint
descriptor. So, it needs to use usb_endpoint_xfer_isoc to judge
ISO XFER.

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Li Yang <leoli@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>