usb: Fail a get config when the port is powered off.

Alan Stern pointed out that a USB port could potentially get powered off
when the attached USB device is in the middle of enumerating, due to
race conditions:
	http://marc.info/?l=linux-usb&m=134130616707548&w=2

If that happens, we need to ensure the enumeration fails.  If a call to
usb_get_descriptor() fails for a reason other than a Stall, return an
error.  That should handle the case where the port is powered off.
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: NSarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/config.c

@@ -702,6 +702,8 @@ int usb_get_configuration(struct usb_device *dev)
 		if (result < 0) {
 			dev_err(ddev, "unable to read config index %d "
 			    "descriptor/%s: %d\n", cfgno, "start", result);
+			if (result != -EPIPE)
+				goto err;
 			dev_err(ddev, "chopping to %d config(s)\n", cfgno);
 			dev->descriptor.bNumConfigurations = cfgno;
 			break;