usb: chipidea: ci_hdrc_imx: remove unused variable 'res'

'res' is not used anywhere, so let's get rid of it.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>