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/net2280.c b/drivers/usb/gadget/net2280.c
index 3c14c4e..db508d0 100644
--- a/drivers/usb/gadget/net2280.c
+++ b/drivers/usb/gadget/net2280.c
@@ -2257,9 +2257,7 @@
 			else
 				dev->gadget.speed = USB_SPEED_FULL;
 			net2280_led_speed (dev, dev->gadget.speed);
-			DEBUG (dev, "%s speed\n",
-				(dev->gadget.speed == USB_SPEED_HIGH)
-					? "high" : "full");
+			DEBUG(dev, "%s\n", usb_speed_string(dev->gadget.speed));
 		}
 
 		ep = &dev->ep [0];