usb: gadget: amd5536udc: remove unused structure member

that member isn't used anywhere in the driver
and be removed with no mercy.
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/gadget/amd5536udc.h

@@ -472,7 +472,6 @@ struct udc_request {
 
 	/* flags */
 	unsigned			dma_going : 1,
-					dma_mapping : 1,
 					dma_done : 1;
 	/* phys. address */
 	dma_addr_t			td_phys;