xhci: For streams the dequeue ptr must be read from the stream ctx

This fixes TR dequeue validation failing on Intel XHCI controllers with the
following warning:

Mismatch between completed Set TR Deq Ptr command & xHCI internal state.

Interestingly enough reading the deq ptr from the ep ctx after a
TR Deq Ptr command does work on a Nec XHCI controller, it seems the Nec
writes the ptr to both the ep and stream contexts when streams are used.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 2c77bf7..d280e92 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -703,6 +703,7 @@
 
 /* deq bitmasks */
 #define EP_CTX_CYCLE_MASK		(1 << 0)
+#define SCTX_DEQ_MASK			(~0xfL)
 
 
 /**