usb: gadget: aspeed: fix stop dma register setting.

The vhub engine has two dma mode, one is descriptor list, another
is single stage DMA. Each mode has different stop register setting.
Descriptor list operation (bit2) : 0 disable reset, 1: enable reset
Single mode operation (bit0) : 0 : disable, 1: enable

Fixes: 7ecca2a ("usb/gadget: Add driver for Aspeed SoC virtual hub")
Cc: stable <stable@vger.kernel.org>
Acked-by: Felipe Balbi <balbi@kernel.org>
Acked-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
Link: https://lore.kernel.org/r/20210108081238.10199-2-ryan_chen@aspeedtech.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/aspeed-vhub/epn.c

@@ -420,7 +420,10 @@ static void ast_vhub_stop_active_req(struct ast_vhub_ep *ep,
 	u32 state, reg, loops;
 
 	/* Stop DMA activity */
-	writel(0, ep->epn.regs + AST_VHUB_EP_DMA_CTLSTAT);
+	if (ep->epn.desc_mode)
+		writel(VHUB_EP_DMA_CTRL_RESET, ep->epn.regs + AST_VHUB_EP_DMA_CTLSTAT);
+	else
+		writel(0, ep->epn.regs + AST_VHUB_EP_DMA_CTLSTAT);
 
 	/* Wait for it to complete */
 	for (loops = 0; loops < 1000; loops++) {