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/Makefile b/drivers/usb/Makefile
index 969b0a5..75eca76 100644
--- a/drivers/usb/Makefile
+++ b/drivers/usb/Makefile
@@ -53,3 +53,5 @@
 obj-$(CONFIG_USB_RENESAS_USBHS)	+= renesas_usbhs/
 obj-$(CONFIG_USB_OTG_UTILS)	+= otg/
 obj-$(CONFIG_USB_GADGET)	+= gadget/
+
+obj-$(CONFIG_USB_COMMON)	+= usb-common.o