greybus: es2: don't protest when getting -ENOENT/ESHUTDOWN USB errors

-ENOENT or -ESHUTDOWN happens when the urbs are being killed from
->disconnect() callback.  Don't complain to userspace about this, as the
user will see this on es2 module removal.

Tested by removing the gb-es2.ko module on both EVT1.5 and qemu with
gbsim. The driver doesn't throw anymore errors like:
"urb cport in error -2 (dropped)".
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: David Lin <dtwlin@google.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/es2.c

@@ -715,6 +715,11 @@ static void cport_in_callback(struct urb *urb)
 	if (status) {
 		if ((status == -EAGAIN) || (status == -EPROTO))
 			goto exit;
+
+		/* The urb is being unlinked */
+		if (status == -ENOENT || status == -ESHUTDOWN)
+			return;
+
 		dev_err(dev, "urb cport in error %d (dropped)\n", status);
 		return;
 	}