wusb: do a proper channel stop

When stopping the WUSB channel the host should send Channel Stop IEs giving
the WUSB Channel Time of the last MMC.  Both WHCI and HWA hosts provide a
channel stop command for this.

Signed-off-by: David Vrabel <david.vrabel@csr.com>

include/linux/usb/wusb-wa.h

@@ -51,6 +51,7 @@ enum {
 	WUSB_REQ_GET_TIME       = 25,
 	WUSB_REQ_SET_STREAM_IDX = 26,
 	WUSB_REQ_SET_WUSB_MAS   = 27,
+	WUSB_REQ_CHAN_STOP      = 28,
 };