usb: Provide usb_speed_string() function

In a few places in the kernel, the code prints
a human-readable USB device speed (eg. "high speed").
This involves a switch statement sometimes wrapped
around in ({ ... }) block leading to code repetition.

To mitigate this issue, this commit introduces
usb_speed_string() function, which returns
a human-readable name of provided speed.

It also changes a few places switch was used to use
this new function.  This changes a bit the way the
speed is printed in few instances at the same time
standardising it.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/usb/gadget/amd5536udc.c b/drivers/usb/gadget/amd5536udc.c
index ded8d6f..4730016 100644
--- a/drivers/usb/gadget/amd5536udc.c
+++ b/drivers/usb/gadget/amd5536udc.c
@@ -3005,13 +3005,8 @@
 
 		/* link up all endpoints */
 		udc_setup_endpoints(dev);
-		if (dev->gadget.speed == USB_SPEED_HIGH) {
-			dev_info(&dev->pdev->dev, "Connect: speed = %s\n",
-				"high");
-		} else if (dev->gadget.speed == USB_SPEED_FULL) {
-			dev_info(&dev->pdev->dev, "Connect: speed = %s\n",
-				"full");
-		}
+		dev_info(&dev->pdev->dev, "Connect: %s\n",
+			 usb_speed_string(dev->gadget.speed));
 
 		/* init ep 0 */
 		activate_control_endpoints(dev);