usb: host: oxu210hp-hcd: Move declaration of 'qtd' into 'ifdef OXU_URB_TRACE'

If we assign 'epnum' during the declaration we can also avoid "ISO
C90 forbids mixed declarations" issues.  So it does looks like we
can have our cake and eat it in this scenario.

Fixes the following W=1 kernel build warning(s):

 drivers/usb/host/oxu210hp-hcd.c: In function ‘submit_async’:
 drivers/usb/host/oxu210hp-hcd.c:2040:19: warning: variable ‘qtd’ set but not used [-Wunused-but-set-variable]
 2040 | struct ehci_qtd *qtd;
 | ^~~

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Rodolfo Giometti <giometti@linux.it>
Cc: "Eurotech S.p.A" <info@eurtech.it>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200702144625.2533530-24-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/oxu210hp-hcd.c

@@ -2037,16 +2037,15 @@ static struct ehci_qh *qh_append_tds(struct oxu_hcd *oxu,
 static int submit_async(struct oxu_hcd	*oxu, struct urb *urb,
 			struct list_head *qtd_list, gfp_t mem_flags)
 {
-	struct ehci_qtd	*qtd;
-	int epnum;
+	int epnum = urb->ep->desc.bEndpointAddress;
 	unsigned long flags;
 	struct ehci_qh *qh = NULL;
 	int rc = 0;
+#ifdef OXU_URB_TRACE
+	struct ehci_qtd	*qtd;
 
 	qtd = list_entry(qtd_list->next, struct ehci_qtd, qtd_list);
-	epnum = urb->ep->desc.bEndpointAddress;
 
-#ifdef OXU_URB_TRACE
 	oxu_dbg(oxu, "%s %s urb %p ep%d%s len %d, qtd %p [qh %p]\n",
 		__func__, urb->dev->devpath, urb,
 		epnum & 0x0f, (epnum & USB_DIR_IN) ? "in" : "out",