USB: rename USB_SPEED_VARIABLE to USB_SPEED_WIRELESS

It's really the wireless speed, so rename the thing to make
more sense.  Based on a recommendation from David Vrabel

Cc: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/usb/ch9.h b/include/linux/usb/ch9.h
index 94012e6..e58369f 100644
--- a/include/linux/usb/ch9.h
+++ b/include/linux/usb/ch9.h
@@ -775,7 +775,7 @@
 	USB_SPEED_UNKNOWN = 0,			/* enumerating */
 	USB_SPEED_LOW, USB_SPEED_FULL,		/* usb 1.1 */
 	USB_SPEED_HIGH,				/* usb 2.0 */
-	USB_SPEED_VARIABLE,			/* wireless (usb 2.5) */
+	USB_SPEED_WIRELESS,			/* wireless (usb 2.5) */
 	USB_SPEED_SUPER,			/* usb 3.0 */
 };