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/composite.c b/drivers/usb/gadget/composite.c
index c77aca1..e74fd55 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -617,25 +617,9 @@
 		result = 0;
 	}
 
-	INFO(cdev, "%s speed config #%d: %s\n",
-		({ char *speed;
-		switch (gadget->speed) {
-		case USB_SPEED_LOW:
-			speed = "low";
-			break;
-		case USB_SPEED_FULL:
-			speed = "full";
-			break;
-		case USB_SPEED_HIGH:
-			speed = "high";
-			break;
-		case USB_SPEED_SUPER:
-			speed = "super";
-			break;
-		default:
-			speed = "?";
-			break;
-		} ; speed; }), number, c ? c->label : "unconfigured");
+	INFO(cdev, "%s config #%d: %s\n",
+	     usb_speed_string(gadget->speed),
+	     number, c ? c->label : "unconfigured");
 
 	if (!c)
 		goto done;