usb: isp1760: Set IRQF_SHARED flag in core code

The IRQF_SHARED flag needs to be set regardless of the bus type. Don't
require glue code to set it manually.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>