Documentation: usb: fix typo in UVC gadgetfs config command

This seems to be a copy&paste error. With the fix the uvc gadget now can
be created by following the instrucitons.
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/usb/gadget-testing.txt

@@ -693,7 +693,7 @@ such specification consists of a number of lines with an inverval value
 in each line. The rules stated above are best illustrated with an example:
 
 # mkdir functions/uvc.usb0/control/header/h
-# cd functions/uvc.usb0/control/header/h
+# cd functions/uvc.usb0/control/
 # ln -s header/h class/fs
 # ln -s header/h class/ss
 # mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p