usb: informative message if no controller

The message 'No working controllers found' provides no clue that this
refers to USB controllers.

Provide a message that refers to USB.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
diff --git a/drivers/usb/host/usb-uclass.c b/drivers/usb/host/usb-uclass.c
index a1cd0ad..a5288eb 100644
--- a/drivers/usb/host/usb-uclass.c
+++ b/drivers/usb/host/usb-uclass.c
@@ -388,7 +388,7 @@
 
 	/* if we were not able to find at least one working bus, bail out */
 	if (controllers_initialized == 0)
-		printf("No working controllers found\n");
+		printf("No USB controllers found\n");
 
 	return usb_started ? 0 : -ENOENT;
 }