usb: gadget: udc: net2280: Declare allow_status_338x as inline

The function is very simple, does not declare any variable and it is
called in the irq path.

The counterpart for net228x is already declared as inline.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>