usb: gadget: udc: lpc32xx: allocate descriptor with GFP_ATOMIC

Gadget drivers may queue request in interrupt context. This would lead to
a descriptor allocation in that context. In that case we would hit
BUG_ON(in_interrupt()) in __get_vm_area_node.

Also remove the unnecessary cast.
Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Tested-by: James Grant <jamesg@zaltys.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/lpc32xx_udc.c

@@ -937,8 +937,7 @@ static struct lpc32xx_usbd_dd_gad *udc_dd_alloc(struct lpc32xx_udc *udc)
 	dma_addr_t			dma;
 	struct lpc32xx_usbd_dd_gad	*dd;
 
-	dd = (struct lpc32xx_usbd_dd_gad *) dma_pool_alloc(
-			udc->dd_cache, (GFP_KERNEL | GFP_DMA), &dma);
+	dd = dma_pool_alloc(udc->dd_cache, GFP_ATOMIC | GFP_DMA, &dma);
 	if (dd)
 		dd->this_dma = dma;