usb/hcd: Fix dma_map_sg error check

dma_map_sg return 0 on error.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Alexey Sheplyakov <asheplyakov@basealt.ru>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Weitao Wang <WeitaoWang-oc@zhaoxin.com>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-usb@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20220819060801.10443-7-jinpu.wang@ionos.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hcd.c

@@ -1474,7 +1474,7 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 						urb->sg,
 						urb->num_sgs,
 						dir);
-				if (n <= 0)
+				if (!n)
 					ret = -EAGAIN;
 				else
 					urb->transfer_flags |= URB_DMA_MAP_SG;