usb: isp1760: do not shift in uninitialized slot

Even though it is not expected, and would trigger a WARN_ON, killing a
transfer in a uninitialized slot this sequence is warned by clang
analyzer, twice:

drivers/usb/isp1760/isp1760-hcd.c:1976:18: warning: The result of the left shift is undefined because the right operand is negative [clang-analyzer-core.UndefinedBinaryOperatorResult]
                skip_map |= (1 << qh->slot);
drivers/usb/isp1760/isp1760-hcd.c:1983:18: warning: The result of the left shift is undefined because the right operand is negative [clang-analyzer-core.UndefinedBinaryOperatorResult]
                skip_map |= (1 << qh->slot);

Only set skip map if slot is active.
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Link: https://lore.kernel.org/r/20210819180929.1327349-5-rui.silva@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/isp1760/isp1760-hcd.c

@@ -1974,16 +1974,20 @@ static void kill_transfer(struct usb_hcd *hcd, struct urb *urb,
 	/* We need to forcefully reclaim the slot since some transfers never
 	   return, e.g. interrupt transfers and NAKed bulk transfers. */
 	if (usb_pipecontrol(urb->pipe) || usb_pipebulk(urb->pipe)) {
-		skip_map = isp1760_hcd_read(hcd, HC_ATL_PTD_SKIPMAP);
-		skip_map |= (1 << qh->slot);
-		isp1760_hcd_write(hcd, HC_ATL_PTD_SKIPMAP, skip_map);
-		ndelay(100);
+		if (qh->slot != -1) {
+			skip_map = isp1760_hcd_read(hcd, HC_ATL_PTD_SKIPMAP);
+			skip_map |= (1 << qh->slot);
+			isp1760_hcd_write(hcd, HC_ATL_PTD_SKIPMAP, skip_map);
+			ndelay(100);
+		}
 		priv->atl_slots[qh->slot].qh = NULL;
 		priv->atl_slots[qh->slot].qtd = NULL;
 	} else {
-		skip_map = isp1760_hcd_read(hcd, HC_INT_PTD_SKIPMAP);
-		skip_map |= (1 << qh->slot);
-		isp1760_hcd_write(hcd, HC_INT_PTD_SKIPMAP, skip_map);
+		if (qh->slot != -1) {
+			skip_map = isp1760_hcd_read(hcd, HC_INT_PTD_SKIPMAP);
+			skip_map |= (1 << qh->slot);
+			isp1760_hcd_write(hcd, HC_INT_PTD_SKIPMAP, skip_map);
+		}
 		priv->int_slots[qh->slot].qh = NULL;
 		priv->int_slots[qh->slot].qtd = NULL;
 	}