usb: doc: rename ci13xxx-imx.txt to ci-hdrc-imx.txt

We have already renamed the file name, change doc name at this
patch.

Cc: devicetree@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>